LIBRARY 


UNIVERSITY  OF  CALIFORNIA. 


• 

Class 


LEAD    REFINING   BY 
ELECTROLYSIS 


BY 

ANSON    GARDNER    BETTS 

i/ 


FIRS  T    EDITION 

FIRST    THOUSAND 


OF  THE 

UNIVERSITY 

OF 


NEW    YORK 

JOHN  WILEY  &  SONS 

London:    CHAPMAN   &   HALL,    Limited 

1908 


wM«4tt*<*  r>»T. 


Copyright,  1908 

nr 
ANSON    G.   BETTS 


Eobwt  Srummonh  anb  Compani} 


PREFACE. 

THE  electrolytic  refining  of  lead  bullion  has  now  become 
an  established  metallurgical  process,  with  further  extensions 
confidently  expected  to  come  from  time  to  time.  Lead 
is  almost  an  ideal  metal  to  refine  electrolytically,  because  its 
electrochemical  equivalent  is  very  high,  and  hence  the  power 
cost  is  small,  and  the  depositing  tanks  are  relatively  smaller 
or  fewer  than  for  other  common  metals.  Its  casting  into 
'anodes  is  especially  easy,  and  it  stands  high  enough  in  the 
electrochemical  scale  to  leave  its  impurities  almost  entirely 
in  the  anode  slime,  as  metals,  so  there  is  no  appreciable  con- 
tamination of  the  electrolyte. 

The  contained  information  is  the  result  of  a  number  of 
years  of  study,  experiment  and  practical  work,  and  is  pub- 
lished in  the  hope  that  it  will  save  those  who  may  be  inter- 
ested in  lead  refining  practice  or  its  improvement  the  re- 
petition of  experiments  already  performed,  and  give  them 
the  benefit  of  the  work  already  done  by  others  and  myself. 
Some  space  has  been  devoted  to  theoretical  discussions  of 
conductivity  of  electrolyte,  etc.,  which  I  thought  would  be 
useful  and  instructive. 

The  variety  of  methods  of  slime  treatment  which  are  dis- 
cussed in  Chapter  II,  may  seem  unnecessarily  large  from  the 
practical  standpoint,  though  I  myself  believe  it  is  desirable 
to  treat  them  at  the  length  I  have.  I  had  some  hesitancy 

iii 


187777 


IV  PREFACE. 

in  including  a  list  of  patents  published,  as  they  are  largely 
my  own,  but  saw  clearly  that  a  treatise  on  this  subject  re- 
quired all  available  information  of  any  importance,  and  would 
be  wanted  by  readers. 

I  wish  to  make  grateful  acknowledgment  to  my  parents, 
Mr.  and  Mrs.  Edgar  K.  Betts,  of  this  city,  for  unfailing  assist- 
ance and  encouragement  while  performing  my  experiments. 
I  am  indebted  for  appreciated  suggestions  and  information 
to  Dr.  E.  F.  Kern  and  Dr.  Wm.  Valentine,  who  have  been 
associated  with  me  in  developing  process  and  plant,  Dr.  Kern 
from  April  1902  to  June  1904,  and  Dr.  Valentine  from  Octo- 
ber 1902  until  now;  to  Messrs.  W.  H.  Aldridge,  John  F.  Mil- 
ler, A.  J.  McNab,  and  Jules  Labarthe  of  Trail;  B.  C.,  Messrs. 
H.  A.  Prosser,  Aug.  E.  Knorr  and  Wm.  Thum,  of  the  United 
States  Metals  Refining  Co.,  and  Messrs.  A.  S.  Dwight  and 
Ernst  F.  Eurich,  and  to  many  others. 

TROY,  NEW  YORK.  September,  1907 


CONTENTS. 


PAGE 

PREFACE  . .  iii 


CHAPTER  I. 

ELECTROLYTES  FOR  LEAD  REFINING 3 

Faraday's  law,  3;  electromotive  forces,  4;  rule  of  electrolytic 
refining,  5 ;  energy  requirements,  6 ;  fused  electrolytes,  7 ;  historical, 
Keith's  process,  10;  Tommasi  process,  Glaser's  experiments,  11; 
development  of  the  Betts  process,  12;  crystallization  prevention, 
14;  current  efficiency  and  gelatine,  16;  conductivity  of  different  elec- 
trolytes, 17;  acid  strength,  18-  various  solutions,  22;  solid  lead 
deposition,  22;  phenolsulphonate  solution,  24;  dithionate  solution, 
25;  preparation  of  dithionates,  26;  fluroborate  solution,  28;  fluo- 
silicic  acid,  29;  lead  fluosilicate  solution,  30;  lead  fluosilicate,  31; 
dissociation  of  the  solution,  32;  losses  of  fluosilicic  acid,  35;  silica 
deposited  in  slime,  36;  acid  loss  on  cathodes,  38;  acid  loss  in  early 
work,  41;  gelatine  or  glue  required,  42;  conductivity,  42;  metals 
present,  46;  Mennicke's  experiments,  47;  tin  in  lead  bullion,  47;  the 
anode  slime,  48;  polarization  of  anode  slime,  49;  e.m.f.'s  of  solution, 
52;  limiting  current  density,  53;  lead  compounds  with  other  metals 
in  slime,  54;  extraction  of  lead  from  very  impure  bullion,  56; 
Senn's  results,  57 ;  iron  and  zinc,  58 ;  preparation  of  pure  lead,  59. 


CHAPTER  II. 

CHEMISTRY  OF  SLIME  TREATMENT 60 

Separation  by  distillation,  60;  analyses,  61;  amalgamation,  62; 
fusion  to  alloys,  63;  removal  of  lead  in  melting,  64;  treatment  of 
slag,  65;  chlorination,  67 ;  chlorination  of  wet  slime,  70 ;  fusion  with 
soda,  71;  process  used  at  Trail,  melting  without  fluxes,  73;  con- 
sideration of  electric  furnaces  for  melting,  74 ;  probable  power  re- 
quired, 75;  products  of  melting,  76;  treatment  of  products,  77; 
melting  with  sulphur,  78;  treatment  of  the  slag,  electrolysis  of  slime 


vi  CONTENTS. 

PAGE 

as  anode,  83;  refining  slime  alloys,  89;  wet  regeneration  process, 
91;  fluosilicate  solutions,  92;  chloride  solutions,  92;  sulphate  solu- 
tions, 93;  fluoride  solutions,  93;  lead  peroxide,  93;  ferric  sulphate 
process,  93;  products,  98;  treatment  of  copper  slime,  100;  electroly- 
sis for  regeneration  of  ferric  sulphate,  102;  influence  of  current 
density,  temperature,  and  relative  motion  of  anodes  and  solution, 
103;  deposition  of  silica  on  the  anodes,  107;  diaphragms,  109; 
extraction  of  the  antimony,  111 ;  addition  of  copper  to  the  solution, 
114;  perfluoride  processes,  115;  antimony  pentafluoride,  118;  use 
of  monobasic  acids,  119;  lead  peroxide,  119;  use  of  fluosilicic  and 
hydrofluoric  acids  together,  120;  treatment  of  air-oxidized  slime, 
121;  alkaline  regeneration  processes,  123;  copper  fluosilicate,  125; 
air  oxidation  of  slime  suspended  in  a  solution,  126 ;  roasting  processes, 
128;  roasting  with  sulphuric  acid  process,  129;  dissolving  air-dried 
slime  in  H2SiF  and  HF,  134;  products  of  electrolysis,  136. 


CHAPTER  III. 

DEPOSITION  OF  ANTIMONY  FROM  THE  FLUORIDE  SOLUTION „-.  r~138 

Electrolytic  refining  of  antimony,  138 ;  deposition  from  the  fluoride 
solutions,  using  insoluble  anodes,  139;  anodes,  140;  anode  reac- 
tions, 141;  efficiency,  143;  anodes  used,  144;  impurities,  144; 
analyses,  146 ;  cost  of  depositing  antimony,  148. 


CHAPTER  IV. 

ELECTROLYTIC  REFINING  OF  DORE  BULLION 149 

Dietzel  process,  150;  refining  with  a  methyl-sulphate  solution, 
152;  Moebius  and  Balbach  apparatus,  155;  use  of  gelatine  to  pro- 
duce solid  silver,  158;  process  used  in  the  Philadelphia  mint,  159; 
costs  Moebius  and  Nebel  process,  159;  plant  at  Monterey,  Mex., 
160;  costs,  163;  Moebius  and  Nebel  apparatus,  164;  attempts  to 
deposit  solid  silver,  166 ;  various  electrolytes,  166 ;  methyl  sulphuric 
167;  comparative  refining  costs.  170. 


CHAPTER  V. 

THE  MANUFACTURE  OF  HYDROFLUORIC  AND  FLUOSILICIC  ACIDS 174 

Testing  fluorspar,  174;  small-scale  work,  174;  retorts,  175; 
condensers,  176;  charge,  176;  analysis  of  products,  177;  con- 
version to  fluosilicic  acid,  178. 


CONTENTS.  vii 

CHAPTER  VI. 

,  PAGE 

CHOICE  OF  CONSTANTS ISO- 
Comparison  of  series  and  multiple  systems,  180;  purity  of  lead, 
182;  cost  of  glue,  183;  current  density,  183;  tank  depreciation, 
185;  acid  loss,  185;  interest  on  conductors,  186;  interest  on  tanks 
and  electrolyte,  186;  power  cost,  187;  final  comparison,  189; 
cost  of  plant,  190;  choice  of  slime  process,  191;  cost  melting  with 
sulphur,  192;  cost  melting  to  dore,  matte,  and  slag,  193;  cost  of 
roasting  with  sulphuric  acid  process,  194;  cost  of  ferric  sulphate- 
process,  195. 


CHAPTER  VII. 

REFINERY  CONSTRUCTION,  OPERATION,  AND  REFINING  COSTS 197 

Levels  in  refinery,  197;  arrangement,  197;  melting  furnaces,  198; 
suggested  improvement  in  melting  cathodes,  198;  dross,  198, 
202;  casting  anodes,  202;  anode. mold,  203;  closed  anode  molds, 
209;  TrusswelFs  mold,  209;  results  in  sampling,  213;  size  of  tanks, 
213;  concrete  tanks,  215;  wood  tanks,  220;  placing  of  bolts,  221; 
arrangement  of  tanks,  223;  cathodes,  228;  casting  cathodes,  231; 
cathode-supporting  bars,  233 ;  foundations  for  tanks,  233 ;  cleaning- 
tanks,  234 ;  contacts,  237 ;  circulation  of  electrolyte,  237 ;  pumps, 
239;  electrolyte,  242;  washing  appliances  for  electrodes,  244; 
washing  slime,  246;  cranes,  250;  floors,  252;  evaporators,  252; 
summary  of  plants,  255;  drying  slime,  256;  melting  slime,  256; 
leaching  slime,  257;  tanks  for  antimony  depositing,  259;  ferric- 
sulphate  tanks,  260;  refinery  management,  267;  cost  of  making 
cathodes,  271;  cost  of  tank-room  labor,  272;  cost  of  handling  lead, 
272;  cost  of  melting  lead,  273;  cost  of  refining  on  a  small  scale, 
273;  comparative  costs  by  the  Parkes  and  Betts  processes,  274; 
cost  of  electrolytic  refinery,  279. 


CHAPTER  VIII. 

PRODUCTS 284 

Analyses  of  bullion  refined  at  Trail,  B.  C.,  284;  analyses  of  Trail 
pig  lead,  284;  analyses  of  lead  refined  by  the  United  States  Metals 
Refining  Co.,  285;  silver  in  pig  lead  at  Trail  in  early  work,  285; 
unequal  distribution  of  silver  in  cathodes,  286;  Trail  refined  lead, 
286;  Trail  bullion,  287;  slime  analyses,  288;  products  of  experi- 
mental refining  at  Troy,  N.  Y.,  289;  lead  in  Japanese  market,  290. 


viii  CONTENTS. 

CHAPTER  IX. 

PAGE 

TREATMENT  OF  LEAD  CONTAINING  BY-PRODUCTS 291 

Refining  copper-lead  alloys,  291;  hard  lead,  293;  gold-lead 
bullion,  294. 

CHAPTER  X. 

ANALYTICAL  METHODS  AND  EXPERIMENTAL  WORK 295 

Analysis  of  slime,  295;  assay  of  dore"  bullion,  297;  analysis  of 
refined  lead,  298;  analysis  of  slag,  302;  analysis  of  electrolyte, 
302;  analysis  of  copper-silver  matte,  303;  determination  of  silica 
in  slime,  304;  analysis  of  antimony  fluoride  solution,  304;  experi- 
mental work,  305. 

CHAPTER  XI. 
BIBLIOGRAPHY  . .  .  309 


APPENDICES. 

APPENDIX  I. 

PLANT   OF   THE    CONSOLIDATED    MINING  AND  SMELTING   COMPANY   OF 

CANADA,  LIMITED,  AT  TRAIL,  BRITISH  COLUMBIA 312 

Location,  312;  power  supply,  312;  electric  machinery,  313; 
subdivision  of  tank  room,  313;  tanks  and  method  of  lining,  314; 
bus-bars,  315;  casting  anodes,  316;  anode  molds,  317;  ^stacking 
anodes  for  crane,  318;  cleaning  scrap,  319;  making  cathodes,  319; 
melting  cathodes,  320;  pumping  lead,  320;  collecting  and  washing 
slime,  321;  report  of  washing,  322;  evaporation  of  wash-water,  323; 
slime  treatment,  323;  sodium  sulphide  extraction,  323;  antimony 
depositing,  324;  drying  and  melting  leached  slime,  325;  fluosilicic 
acid  plant,  326 ;  labor  required,  326;  electrolyte,  328;  daily  report, 
329. 

APPENDIX  II. 

REFINING   PLANT  OF  THE   UNITED   STATES   METALS   REFINING 

COMPANY  AT  GRASSELLI,  LAKE  COUNTY,  INDIANA 343 

Buildings,  343 ;  power  plant,  343 ;  tank  arrangement,  343 ;  tanks, 
344;  cranes,  344;  bus-bars,  345;  anodes,  345;  melting  furnaces, 


CONTENTS. 

345;  washing  cathodes,  345;  melting  cathodes,  346;  colllecting 
and  washing  slime,  346;  evaporation  of  wash-water,  346;  electro- 
lyte, 346. 

APPENDIX  III. 

TREATMENT    OF    LEAD-REFINERY    SLIME    WITH    SOLUTION    OF    FERRIC 

FLUOSILICATE  AND  HYDROFLUORIC  ACID 355 

Scale  of  operation,  355 ;  process  used,  356 ;  unsuccessful  electroly- 
tic deposition  of  copper  and  antimony,  356;  use  of  hydrofluoric 
acid  in  solution,  357 ;  advantages  of  process,  357 ;  carbon  diaphragm, 
357;  slime  treated,  358;  description  of  tanks,  360;  ferric-iron 
producing  tank,  361;  solution,  362;  results  in  depositing  copper- 
antimony  and  arsenic,  363;  results  with  ferric-iron  tank,  364; 
treatment  of  slime,  366;  extraction  of  metals,  367,  no  recovery  of 
SiF6  from  slime,  367;  improvements  in  apparatus,  368;  metal  from 
copper-depositing  tanks,  370;  direct  precipitation  of  copper  from 
the  solution,  370;  results,  371;  precipitation  of  arsenic  and  anti- 
mony by  lead,  371;  products  of  precipitation  by  granular  lead, 
374,  375 ;  behavior  of  bismuth  in  precipitators,  376 ;  separation  of 
arsenic  and  antimony,  377;  distinction  of  products,  378;  slime 
treatment,  378;  results  of  slime  treatment,  379;  influence  of  HF 
in  solution,  380;  cotton  diaphragms,  381;  cathodes,  381;  slime 
treatment,  382;  proper  use  of  precipitators,  382. 


LEAD  REFINING  BY  ELECTROLYSIS. 


CHAPTER  I. 

ELECTROLYTES  FOR  LEAD  REFINING. 

WHEN  two  pieces  of  the  same  metal  are  dipped  into  a 
solution,  no  difference  of  electro-motive  force  is  produced 
between  the  metals,  as  when  dissimilar  metals  like  zinc  and 
copper  are  immersed.  When  an  appropriate  solution  is  used 
and  the  pieces  of  metal  (electrodes)  are  placed  in  an  electric 
circuit,  metal  may  be  dissolved  from  one  electrode  and  de- 
posited on  the  other.  The  quantities  of  the  various  metals 
transported  by  a  certain  current  in  a  certain  time  are  pro- 
portional to  the  atomic  weight  of  the  metal,  divided  by  the 
valency  in  which  it  exists  in  the  solution  (Faraday's  law). 
These  quantities  are,  per  ampere  hour,  for  a  few  metals  of 
interest  to  lead  refining,  as  follows. 


TABLE  1. 

Silver 4.025  grams  per  amp.  hr. 

Lead 3.857 

Bismuth 1.948 

Antimony 1 . 494 

Copper  (Cuprous) 2.372 

Copper  (Cupric) 1 . 186 

Tin 1.105 

Iron 1 . 044 

Gold  (Auric) 2.452 


4 . 7    amp.  days  per  Ib. 

4.9  " 

9.7 
12.7 

7.95 
15.9 
17.1 
18.1 

7.7 


4  LEAD   REFINING   BY  ELECTROLYSIS. 

As  a  general  thing,  by  using  an  appropriate  solution,  the 
deposited  metal  (cathode)  is  pure,  although  the  dissolved 
metal  (anode)  may  be  very  impure,  and  on  this  fact  electrolytic 
refining  depends. 

Solutions  containing  a  salt  of  the  above  metals,  generally 
with  free  acid  also  present,  have  been  used  almost  entirely 
as  electrolytes.  Some  of  the  metals  can  be  got  into  alkaline 
solution,  for  example,  silver,  lead,  and  copper,  and  some  alka- 
line solutions  are  used  in  electroplating,  but  such  solutions- 
are  not  used  in  refining,  so  far. 

Only  those  metals  which  do  not  dissolve  with  evolution 
of  hydrogen  on  immersion  in  the  refining  solution  have  been 
successfully  refined  up  to  the  present  time.  For  metals  which 
cannot  be  successfully  treated  wet,  as  sodium  and  aluminum, 
fused  electrolytes  are  used. 

The  deposition  of  pure  metals  depends  on  the  fact  that 
each  metal  has  its  own  electromotive  force  of  solution.  The 
electromotive  force  of  solution  varies  a  few  hundredths  of 
a  volt  for  differences  in  the  concentration  of  the  solution,  and 
is  somewhat  different  for  different  electrolytes.  An  approxi- 
mation is  given  in  Table  2.  This  table  is  practically  correct 
for  fluosilicate  solution. 

TABLE  2. 

Zinc +  .52  volts 

Cadmium +  .  16 

Iron +  .  09 

Lead -.01 

Tin -.01 

Arsenic —  .  40 

Antimony —  .  44 

Bismuth —  .  48 

Copper  (Cupric) —  .  52 

Silver -.97 

Mercury —  .  98 


ELECTROLYTES   FOR   LEAD   REFINING.  5 

The  electromotive  force  of  solution  may  be  defined  as  that 
difference  of  voltage  which  exists  between  an  element  and 
the  solution  also  containing  the  metal  in  which  it  is  immersed. 
An  electric  current  may  be  flowing  in  either  direction  from 
the  electrode  and  solution,  either  depositing  or  dissolving 
metal,  without  changing  the  value  of  this  electromotive  force 
to  any  more  than  a  slight  extent. 

The  results  of  this  are  (1)  that  with  an  anode  containing 
a  considerable  proportion  of  that  one  of  the  metals  present 
in  the  anode,  which  stands  highest  in  the  series  and  therefore 
requires  the  least  application  of  electromotive  force  to  bring 
it  into  solution,  only  that  metal  will  dissolve,  and  those  lower 
in  the  series  will  remain  in  the  metallic  state,  and  (2)  given 
in  the  electrolyte  a  considerable  amount  of  that  metal  which 
has  the  lowest  electromotive  force  of  those  in  the  solution, 
only  that  metal  will  deposit,  the  electromotive  force  at  the 
cathode  being  insufficient  to  deposit  the  others. 

The  rule  of  electrolytic  refining  is  then,  that  the  metals 
lower  in  the  scale  than  the  principal  metal  present,  are  elim- 
inated as  metal  particles  in  the  anode  slime,  and  the  ones  higher 
in  the  series  are  eliminated  as  salts  dissolved  in  the  solution 
or  precipitated  from  it. 

The  elimination  as  metal  in  the  anode  slime  is  the  best 
of  the  two,  as  an  increasing  concentration  of  other  metals 
in  the  solution  requires  a  change  of  electrolyte,  which  is 
troublesome.  For  instance,  in  electrolytic  silver  refining,  the 
principal  impurity,  copper,  dissolves  from  the  anode  and 
collects  in  the  solution,  while  the  percentage  of  silver  gets 
less. 

Lead,  on  the  other  hand,  stands  higher  in  the  scale  than 
all  the  impurities  it  contains  in  appreciable  quantities,  so  that 


6  LEAD   REFINING   BY   ELECTROLYSIS. 

the  solution  does  not  need  to  be  changed.  Taking  this  into 
consideration,  with  the  great  ease  of  casting  lead  into  anodes, 
and  melting  cathodes,  the  comparatively  large  quantity  trans- 
ported by  the  current,  so  that  a  relatively  small  amount  of 
power  is  necessary  and  the  production  is  rapid,  lead  has  the 
most  favorable  physical  and  electrochemical  constants  for 
electrolytic  refining  of  all  the  common  metals. 

With  an  anode  of  composite  metals,  we  do  not  have,  in 
general,  a  mixture  from  which  one  or  more  metals  may  be  dis- 
solved, leaving  the  other  metal  or  metals  in  the  pure  state, 
but  a  mixture  of  different  compounds  of  the  metals  between 
themselves.  The  electromotive  force  of  solution  of  lead 
combined  with  antimony  for  example,  is  less  than  that  of 
pure  lead.  The  result  is  that  in  the  electrolytic  refining  ef 
alloys  we  do  not  have  the  full  difference  in  electromotive 
forces  of  the  metals  available  for  making  a  complete  sepa- 
ration. The  difference  in  electromotive  force  between  lead 
and  the  impurities  is  though,  considerable  enough  to  leave 
something  remaining  after  allowing  for  the  combining  force  of 
lead  and  the  impurities.  The  strength  of  these  combina- 
tions varies  from  practically  no  combination  in  the  case  of 
lead  and  copper  to  quite  a  considerable  one  in  the  case  of 
lead  and  antimony. 

The  transport  of  a  pure  metal  from  one  pure  electrode  to 
another  in  the  same  physical  condition,  through  a  solution, 
Tequires  very  little  energy,  provided  time  is  no  object.  The 
metal  of  the  anode  may  be,  though,  in  a  harder  or  softer  con- 
dition, or  may  not  be  the  simple  metal,  but  may  rather  con- 
sist of  a  series  of  compounds  with  other  metals  present  as 
impurities.  The  elements  in  these  compounds  and  aggrega- 
tions in  general  are  so  weakly  united,  that  usually  the  energy 


ELECTROLYTES    FOR   LEAD   REFINING.  7 

requirement  for  their  decomposition  per  ton  of  anode  is  prac- 
tically negligible.  An  exception  may  be  noted  in  the  case 
of  lead-antimony  alloys,  "hard  lead";  to  extract  the  last  of 
the  lead  from  the  antimony  requires  an  e.m.f.  of  over  .2  volt. 
The  nature  of  these  compounds  is  of  interest  as  the  anode 
slime  probably  consists  of  a  mixture  of  them. 

The  question  of  time  is,  however,  one  of  the  most  im- 
portant factors,  for  the  refining  capacity  of  a  plant  of  given 
size  varies  inversely  with  the  speed  of  working.  As  we  can 
only  afford  to  use  a  reasonable  amount  of  electric  energy  per 
ton  refined,  the  first  consideration  is  to  find  an  electrolyte  of 
as  high  an  electric  conductivity  as  possible. 

The  best  conducting  electrolyte  will  be  found  with  a  melted 
salt,  and  melted  lead  chloride  is  an  exceptionally  good  con- 
ductor. 

At  580°  C.,  according  to  Kohlrausch,  PbCU  has  a  resist- 
ance of  .0373  ohms  for  a  column  1  sq.  decimeter  by  1  deci- 
meter =.095  ohms  per  column  1  sq.  inch  by  1  inch.  For  com- 
parison, the  aqueous  electrolyte  used  with  a  resistance  of 
1.3  —  1.4  ohms  is  about  fourteen  times  a  poorer  conductor. 
With  the  fused  electrolyte  and  the  same  voltage  and  separa- 
tion of  electrodes,  the  current  density  would  be  about  210 
amperes  per  square  foot,  a  4000  ampere  vat  requiring  then 
about  19  sq.  ft.  of  surface.  The  expenditure  of  1-1.5  kilowatt 
would  not  keep  an  apparatus  of  this  size,  or  of  one  anywhere 
nearly  as  large,  at  a  red  heat,  and  li  kw.  is  about  all  the 
power  used  for  a  4000  ampere  tank.  It  is  doubtful  if  one 
kw.  would  keep  an  apparatus  occupying  more  than  a  few  cubic 
inches  at  the  necessary  temperature. 

Fused  lead  chloride  dissolves  lead  sulphide  and  also  gives 
a  low  melting,  high-conductivity  electrolyte,  which,  how- 


8  LEAD   REFINING    BY   ELECTROLYSIS. 

ever,  could  not  be  as  good  as  lead  chloride  alone.  Lead 
fluoride  I  have  tried  to  use  as  an  electrolyte  in  decomposing 
lead  sulphide,  but  it  is  relatively  infusible. 

Lead  chloride  melts  at  a  moderate  heat,  stated  in  places 
to  be  about  500°  C.  Provided  a  suitable  tank  could  be  found, 
if  it  was  attempted  to  use  fused  lead  chloride  with  the  usual 
depending  electrodes,  of  course  they  would  melt  off,  and  the 
loss  of  heat  would  be  enormous  too, 

Mr.  R.  H.  Sherry  made  an  experiment  in  my  laboratory 
with  a  mixture  of  fused  zinc  and  lead  chloride,  melting  below 
the  melting-point  of  lead,  so  that  solid  lead  electrodes  could 
be  used.  The  resistance  of  zinc  chloride  is  given  by  Kohl- 
rausch  as  10.98  ohms  per  cubic  decimeter,  =  27.9  per  cubic 
inch.  The  resistance  in  Mr.  Sherry's  experiment  was  at  310°  C. 
about  2.5  ohms  per  cubic  inch,  or  greater  than  the  aqueous 
electrolytes. 

Special  apparatus  would  have  to  be  devised  and  the 
current  density  would  have  to  be  far  increased  beyond 
the  10-15  amperes  per  square  foot  used  with  solutions,  to 
reduce  the  radiating  and  heat-conducting  cross-sectional  area 
sufficiently,  and  this  increase  of  current  strength  would  off- 
set to  a  greater  or  less  degree,  probably  greater,  the  advantage 
of  high  conductivity. 

Special  apparatus  has  been  devised  or  suggested  by  Bor- 
chers  *  and  Ashcroft  f  for  refining  lead  with  fused  electrolytes. 

The  use  of  a  mixture  of  lead  chloride  and  oxy-chloride 
was  proposed  by  Prof.  Borchers,*  the  idea  being  that  such  a 
mixture  does  not  attack  iron,  while  the  chloride  does.  The 


*  Electrometallurgy,  1st  English  Edition,  page  338. 

t  Electrochem.  and  Metal  Ind.,  Vol.  IV  (1906),  page  357. 


ELECTROLYTES   FOR   LEAD    REFINING. 

crude  lead  was  allowed  to  flow  from  groove  to  groove  down 
one  side  of  an  iron  vessel  as  anode,  with  an  iron  cathode  at 
the  other  side,  from  which  the  deposited  lead  ran  down  to  a 
separate  collecting  space.  Prof.  Borchers  stated  that  the 
result  in  refining  lead  and  bismuth  alloys  was  excellent,  which 
I  can  well  believe  as  far  as  the  chemical  result  is  concerned, 
but  that  is  probably  about  the  only  use  to  which  the  process 
could  be  put.  After  the  lead  has  been  largely  removed  from 
this  particular  anode  metal  it  is  as  fusible  and  liquid  as  before, 
if  not  more  so,  but  ordinary  crude  lead  and  bullion  on  the 
other  hand  would  get  thicker  and  less  fusible  from  the  accu- 
mulation of  copper  and  arsenic,  silver  and  antimony,  and 
would  soon  be  too  thick  to  be  handled  in  this  way,  long  before 
a  large  part  of  the  lead  could  be  removed.  Futher,  it  would 
take  some  experimental  labor  to  determine  whether  all  the 
impurities  were  separated,  notably  the  arsenic  and  antimony. 
It  is  also  to  be  much  doubted  whether  the  power  cost  could 
be  bought  as  low  as  by  the  wet  process. 

Ashcroft  has  proposed  to  make  the  melted  lead  alloy,  con- 
tained in  a  pot,  anode,  and  spin  a  cathode  of  metal  above 
the  surface  of  the  anode,  and  very  near  it.  The  lead  deposited 
on  the  cathode  is  to  remain  suspended  by  the  action  of  a 
magnetic  field,  instead  of  dropping  back  into  the  anode  metal. 
The  magnetic  field  is  to  rotate  the  conducting  cathode,  which 
it  might  do,  but  the  action  on  the  lead  on  the  underside  of 
the  cathode,  if  there  were  any  action  in  practice,  could  not 
act  to  support  this  lead,  but  only  to  move  it  in  a  horizontal 
circle,  the  same  as  the  cathode  itself. 

There  will  be  a  difficulty  in  making  the  surface  of  the 
anode  metal  lie  flat,  as  the  metal  will  tend  to  move  in  a  circle 
too,  from  friction  and  perhaps  from  magnetism  in  connection 


10  LEAD    REFINING   BY   ELECTROLYSIS. 

with  the  current  passing  through.  The  same  trouble  I  men- 
tioned before  with  the  impurities  of  the  lead  will  also  appear 
here,  to  a  more  serious  extent,  as  the  impurities  are  lighter 
than  lead,  and  as  the  lead  was  removed  would  form  a  scum 
on  its  surface. 

The  inevitable  difficulty  with  the  accumulating  impuri- 
ties of  the  lead  in  such  methods  and  other  serious  difficulties, 
made  the  wet  method  always  seem  the  best.  Since  the  power 
cost  per  ton  of  lead  with  the  cheap  electric  power  now  avail- 
able (and  this  will  probably  be  cheaper  as  time  goes  on),  is 
only  about  50  cents,  a  great  saving  is  not  possible  anyway. 

The  historical  development  of  electrolytic  lead  refining, 
up  to  my  own  work,  is  given  by  Messrs.  Watt  and  Philip  in 
their  book,  "  Electroplating  and  Electrorefining."* 

Prof.  N.  S.  Keith  as  early  as  1878  developed  his  process 
of  refining  lead,  with  an  electrolyte  containing  180  grams 
sodium  acetate  per  litr'fc,  in  which  was  dissolved  18.5  to  22.2 
grams  of  lead  sulphate  per  litre.  He  used  20  Ib.  anodes, 
15X24  inches,  and  J  to  ^  inches  thick,  wrapped  in  muslin 
cloths  to  catch  the  anode  slime,  which  would  otherwise  drop 
to  the  bottom  of  the  tank  with  the  refined  lead  crystals  fall- 
ing from  the  cathodes. 

At  Rome,  N.  Y.,  a  plant  was  built  with  30  tanks  produc- 
ing 3  tons  of  lead  per  day  of  twenty-four  hours.  The  tanks 
were  circular,  made  of  a  kind  of  concrete  mixture,  6  feet  in 
diameter,  40  inches  deep,  with  a  central  pillar  2  feet  in  diam- 
eter occupying  the  centre  of  the  tank.  Brass  cylindrical 
cathodes  were  used  2  inches  apart,  and  extended  all  the  way 
round  the  tank,  with  270  anode  plates  to  the  tank  6X24 

*  New  York  and  London,  1902. 


ELECTROLYTES   FOR   LEAD   REFINING.  11 

inches,  and  weighing  8  Ibs.;  current  was  supplied  by  an  Edison 
dynamo  of  2000  amperes  and  10  volts.  The  anodes  were 
hung  from  a  frame  which  rotated  continuously  and  carried 
scrapers  that  scraped  the  deposited  lead  from  the  cathodes. 
The  current  density,  calculated  from  these  figures,  was  3.2 
amperes  per  square  foot. 

Tommasi  *  published  various  articles  in  1897  and  1898 
describing  his  arrangement  for  refining  lead,  also  with  the 
acetate  solution.  His  proposition  was  to  use  as  a  cathode  a 
circular  aluminum-bronze  disc,  mounted  on  a  shaft  just  above 
the  top  of  the  electrolytic  cell,  which  disc  was  to  turn  once 
a  minute,  and  be  relieved  of  its  deposit  of  spongy  lead  by  a 
scraper  above  the  tank,  while  the  spongy  lead  was  automati- 
cally carried  off  to  a  press.  Tommasi,  in  elaborate  but  wrong 
calculations,  presumes  a  refining  cost  of  8.6  francs  per  metric 
ton  with  steam  power  and  5.8  francs  with  water  power.  The 
process  described  would,  however,  j)^Rbably  cost  nearer  50 
or  75  francs,  if  all  went  well.  #r 

L.  Glaser  f  reports  a  number  of  experiments  with  little 
exactness  of  description,  in  depositing  lead  from  various 
electrolytes,  the  description  being  limited  to  lead  nitrate, 
lead  nitrate  and  sodium  nitrate,  lead  acetate,  sodium  nitrate 
saturated  with  lead  hydrate,  and  caustic  potash  with  lead 
hydroxide  in  solution  of  various  strengths,  and  claims  a  solid 
lead  deposition.  I  have  repeated  Glaser's  experiments  very 
fully  as,  -far  as  it  is  possible  to  follow  him,  and  in  no  case 
I  able  to  get  a  solid  deposit  of  any  measurable  thickness. 


*  Comptes  Rendus,  1896,  Vol.  122,  p.  1476.  Zeitschrift  f  iir  Electrochemie, 
Vol.  3,  92,  310,  341. 

f  Zeitschrift  fur  Electrochemie.  1900,  Vol.  7  (24),  365-369  and  (26) 
381-386. 


12  LEAD   REFINING   BY   ELECTROLYSIS. 

Following  a  work  of  Foerster  and  Guenther,  who  offered 
the  explanation  that  spongy  zinc  deposits  are  caused  by  the 
simultaneous  deposition  of  zinc  oxide  with  the  zinc,  Glaser 
attempts  to  prove  the  cause  of  the  loose  lead  deposit  to  be 
due  to  the  co-deposition  of  lead  hydroxide.  This  is,  how- 
ever, incorrect  theory,  as  anyone  can  easily  see  by  electro- 
lyzing  lead  solutions  containing  free  acid,  as  nitric,  acetic, 
fluosilicic,  etc.,  which  by  their  acidity  absolutely  prevent  the 
separation  of  lead  hydroxide,  and  yet  give  loose  deposits. 
It  is  also  possible,  without  making  any  alteration  of  the 
acidity  of  a  proper  solution,  to  cause  the  separation  of  a 
solid  instead  of  incompact  deposit,  as  will  be  seen  later. 

The  next  proposition  for  refining  lead  is  seen  in  patent 
specifications.*  I  refined  about  half  a  ton  of  lead,  in  4  cells 
each  10J"  wide,  16"  deep,  and  30"  long,  containing  9  anodes 
weighing  about  12  Ibs.  each,  and  10J  inches  wide  by  13J 
inches  deep.  The  strength  of  the  solutions  varied  from  4 
to  20  grams  lead  and  12  to  25  grams  SiF6  per  100  cc.,  but  the 
deposit  was  ajways  incompact.  The  cathodes  consisted  of 
sheet  iron,  which  it  was  attempted  to  coat  with  lead  by 
dipping  into  lead  in  a  deep  pot,  and  afterward  by  lead- 
plating  them.  In  the  first  experiments  the  idea  was  to 
simply  melt  the  lead  off  the  iron  when  the  cathodes  were 
finished,  by  dipping  into  melted  lead,  after  which  the  cathodes 
could  be  returned  to  the  tanks.  In  the  later  experiments 
the  cathodes  were  greased  and  the  lead  afterward  peeled  off 
mechanically. 

Every  few  hours  during  the  runs,  which  lasted  during  the 


*U.  S.  Patents,  A.  G.  Belts;  679,357,  July  30,  1901;  679,824  August  6, 
1901. 


ELECTROLYTES   FOR   LEAD   REFINING.  13 

•day  time  for  about  a  week,,  with  a  current  from  120-150 
amperes  (  =  7  to  8.8  amperes  per  square  foot,  total  e.m.f.  per 
cell  0.175  volts),  the  cathodes  were  taken  out  and  passed 
through  steel  rolls  of  about  3"  diameter.  The  sheets  came 
through  the  rolls  in  quite  a  solid  deposit  and  with  a  smooth 
surface.  A  good  deal  of  electrolyte  was  squeezed  out  and 
part  of  this  was  lost,  and  the  whole  was  a  disagreeable  job 
with  the  machinery  at  hand.  A  sample  of  the  deposit, 
which  seemed  quite  solid,  showed  a  specific  gravity  of  10.28 
only,  against  11.36  to  11.40  for  pure  lead.  This  would 
mean  a  loss  of  electrolyte  in  the  remaining  pores,  per  ton 
refined,  of  about  .3  cubic  foot,  still  a  rather  serious  item. 

The  idea  was  to  equip  the  tanks,  as  may  be  seen  from 
the  above-mentioned  patents,  with  a  pair  of  rails  on  each 
side,  over  which  ran  a  machine  that  automatically  stopped 
over  each  cathode  in  succession,  raised  it  through  a  pair  of 
rolls  and  returned  it  to  its  position  in  the  tank. 

TABLE  3. 
ANALYSES  OF  BULLION  TREATED  AND  REFINED  LEAD  PRODUCED. 

Bullion.  Refined  Lead.  Slime. 

Ag  about  .50%  Ag  .0003%  Ag  36.4% 

Cu      "  .31%  Cu  .0007%  Cu  25.1% 

Sb      "  .43%  Sb  .0019%  Sb  29.5% 

Pb      "  98.76%  Pb  99.9971%  Pb  9.0% 


Bullion.  Refined  Lead. 

Cu 75     %  Cu  .0027% 

Bi 1 .22     %  Bi  .0037% 

As 936%  As  .0025% 

Sb 6832%  Sb  .0000% 

Ag 358.89  oz.  Ag  .0010% 

Au 1 . 71  oz.  Au         None 

Fe  .0022% 

Zn  .0018% 


14  LEAD   REFINING   BY   ELECTROLYSIS. 

The  idea  of  using  rails  at  the  side  of  the  tanks,  over 
which  carriages  may  be  run  to  carry  electrodes  in  and  out 
and  slime  out,  seems  to  be  one  that  might  be  adopted  in 
refineries  with  some  advantage. 

The  objection  to  a  loose  mass  of  separate  lead  crystals, 
as  previously  invariably  produced  in  electrolyzing  lead  solu- 
tions, is  serious  from  the  refining  standpoint.  After  doing 
considerable  work  with  mechanical  methods  of  compacting 
the  lead,  I  discovered  certain  materials  that,  if  added  to  such 
a  solution  as  the  fluosilicate,  caused  the  production  of  solid 
lead  deposits,  notably  gelatine  and  pyrogallol,  although  when 
added  to  acetate  solutions  they  had  no  valuable  effect.  As 
gelatine  is  the  cheapest,  it  alone  has  been  adopted  in  prac- 
tice. Saligenin  and  resorcin  were  found  to  cause  an  im- 
provement, but  not  quite  so  solid  a  deposition  as  the  other 
two.  The  search  was  not  limited  to  organic  reagents,  but 
they  alone  were  found  suitable.  With  the  addition  of  small 
amounts  of  gelatine  to  a  fluosilicate  solution,  perhaps  1  part 
of  gelatine  to  5000  or  less  parts  of  solution,  the  lead  sepa- 
rates as  a  solid  smooth  deposit,  with  a  specific  gravity  of 
11.3  to  11.4,  the  same  as  cast  lead. 

The  way  in  which  the  gelatine,  etc.,  bring  about  this  re- 
markakle  result  is  hard  to  trace.  I  am  satisfied  that  the 
next  step  toward  a  complete  explanation  is  to  be  found  in 
variation  in  hardness  or  tensile  strength  of  the  cathode  deposit 
resulting  from  the  use  of  gelatine,  etc.  The  principal  rea- 
sons for  this  opinion  are  based  on  these  facts: 

1.  *  Although  equally  pure,  the  solid  electrolytic  lead 
deposit  is  several  times  stronger  than  ordinary  lead. 

*  Belts,  Trans.  Am.  Electrochem.  Soc.      Vol.  VIII,  1905,  page  83. 


ELECTROLYTES    FOR   LEAD   REFINING.  15 

2.  The  greater  the  tension  at  the  surface  of  an  electro 
deposit,  the  greater  the  tendency  to  keep  the  new  surface 
forming  smooth.* 

3.  Lead  deposited  from  liquids  in  which  its  surface  ten- 
sion after  immersion  must  be  greater,  is  smoother,  e.g.,  pyri- 
dine  solutions.! 

4.  Strong  metals,  otherwise  suitable  for  electro-deposition, 
give  the  smoothest  deposits.    Weak  metals  give  loose  crys- 
talline growths. 

In  what  way  the  gelatine  or  other  similar  addition  acts 
to  increase  the  strength  of  the  surface  layer  of  cathode 
deposit  has  not  been  definitely  established. 

It  is  an  interesting  fact  that  the  addition  of  gelatine  or 
pyrogallol  to  the  acetate  and  similar  solutions  does  not 
cause  the  production  of  a  solid  deposit,  while  the  addition 
of  gelatine  in  the  strong-acid  solutions,  fluosilicic,  fluoboric, 
etc.,  does. 

Snowdon  claims  to  mechanically  produce  solid  lead  from 
the  acetate  solution  by  the  use  of  a  rapidly  revolving  cathode, 
but  does  not  give  the  specific  gravity  of  the  product. J 

I  criticize  the  practice  of  describing  lead  deposits  as 
solid,  homogeneous,  etc.,  without  making  any  definite  state- 
ments as  to  the  specific  gravity,  mechanical  soundness,  etc. 
Some  definite  standard  is  required  to  show  how  "  solid"  a 
deposit  is,  also  the  thickness  of  the  deposit  should  be  detailed. 
Many  deposits  of  slight  thickness  have  quite  a  smooth  and 
solid  appearance  for  that  reason,  but  after  building  them  up 
a  little  more,  their  true  loose  nature  can  be  recognized. 


*  Betts,  Trans.  Am.  Electrochem.  Soc.     Vol.  VIII,  1905,  page  85. 

f  Kahlenberg,  Trans.  Am.  Electrochem.  Soc.     Vol.  VI,  1904,  page  40. 

j  Trans.  Am.  Electrochem.  Soc.     Vol.  IX,  1906,  page  221. 


16 


LEAD   REFINING    BY   ELECTROLYSIS. 


The  lead  deposit  forming  in  lead  fluosilicate-fluosilicic 
acid  solutions,  containing  .1%  of  gelatine,  and  five  or  more 
per  cent  lead,  is  smooth  and  solid,  and  thick  pieces  cut  from 
the  deposit  show  a  specific  gravity  of  11.35  to  11.40;  the 
same  metal  after  melting  and  casting  shows  practically  the 
same  specific  gravity,  in  some  cases  exactly  the  same.  With 
a  little  more  lead,  say  7-8%,  and  the  average  current  density 
employed  in  commercial  operations  of  15  amperes  per  square 
foot,  the  resulting  cathodes,  after  reaching  a  considerable 
thickness,  are  smoother.  The  electrochemical  equivalent  of 
lead  is  so  high  that  with  only  5%  lead,  the  layer  in  the  imme- 
diate neighborbood  of  the  cathode  is  probably  nearly  ex- 
hausted in  respect  to  lead,  and  if  the  lead  is  allowed  to  go 
much  below  4%,  a  black,  slimy  deposit  of  lead  is  the  result. 
bThat  gelatine  does  not  affect  the  current  efficiency  I 
determined  some  years  ago  in  the  following  way.  ^Two  solu- 
tions were  electrolyzed  in  series,  one  containing  gelatine  and 
the  other  without. 

TABLE  4. 


Experiment 
No. 

Without  Gelatine. 

With  Gelatine. 

Weight 
Deposited. 

Weight 
Dissolved. 

Weight 
Deposited. 

Weight 
Dissolved. 

1 
2 

4  .  06  gr. 
24.70gr. 

4.06gr. 
24.89gr. 

4  .  04  gr. 
24.72gr. 

4.06gr. 
24.90gr. 

The  electrodes  were  arranged  to  be  weighed  without  re- 
moving them  from  the  solution  at  all,  to  avoid  the  disturb- 
ing influence  of  air  oxidation  on  the  spongy  deposit  from  the 
solution  with  no  gelatine. 

The  amount  of  lead  transported  by  the  current  has  been 


ELECTROLYTES   FOR   LEAD   REFINING.  17 

made  a  careful  study.*  Under  the  most  perfect  conditions 
yet  applied  to  the  deposition  of  lead,  the  electrochemical 
equivalent  of  lead  is  found  to  be  103.43,  that  is,  the  atomic 
weight  of  lead  corresponding  is  206.86  and  the  amount  of 
lead  transported  per  ampere  hour  is  3.857  grams,  f 

For  refining  lead,  we  require  a  solution  of  as  high  a 
conductivity  as  is  commercially  available,  which  also  will 
contain  at  least  several  percent  of  combined  lead  without 
being  saturated  with  the  lead  salt.  Certain  acids,  such  as 
fluosilicic,  fluoboric,  dithionic,  various  fatty  sulphuric  acids, 
as  ethyl-sulphuric  acid,  and  phenol-sulphonic  and  benzene 
sulphonic  acids,  have  been  found  to  meet  the  requirements 
of  high  electric  conductivity  and  solubility  of  their  lead  salts. 

For  a  comparison  of  the  conductivity  of  these  acids  with 
the  acetate  electrolytes  of  Keith  and  Tommasi,  see  Table  5. 

TABLE  5. 

Approximate 
In  100  c.c.  Solution.  Name.  Temperature.       Resistance 

per  Inch  Unit. 

7.7%  Pb  (C2H3O2)2 Acetate 19.6°  C.  75      ohms. 

$14.5%  Pb  (C2H3O2)2 Acetate 19.4°  C.  58 

5  gr.  Pb,  7  gr.  BF4 Fluoborate 25    °  C.  4 

5  gr.  Pb,  15.7  gr.  C6H5SO3 Benzenesulphonate.  .25    °  C.  2.7 

5  gr.  Pb,  12.5  gr.  C2H3SO4 Ethylsulphate 25    °  C.  3.6 

5  gr.  Pb,  9.5  gr.  C2H3O2 Acetate 25    °  C.  84 

15.7   gr.    Pb,   2.4   gr.    K,   and 

21.4  gr.  C2H3O2. Acetate 26    °  C.  22 

Considerations  of  cost  so  far  have  required  the  use  of 
fluosilicic  acid,  but  dithionic  acid  may  yet  be  found  to  be 
more  economical. 

Several  recent  writers  have  apparently  thought  that 
fluosilicic  acid  had  some  peculiar  property  that  made  it  better 

*  Betts  and  Kern,  Trans.  Am.  Electrochem.  Soc.      Vol.  IV,  1904,  page  67. 
f  F.  W.  Clarke,  Trans.  Am.  Chem.  Soc.     Vol.  XXVIII,  1906,  page  307. 
J  Kalender  fur  Elektrochemiker,  1903.     Neuberger. 


18  LEAD   REFINING   BY   ELECTROLYSIS. 

than  other  acids  for  giving  a  solid  lead  deposit.  Mr.  Senn  * 
in  his  paper  describes  experiments  to  see  if  it  was  also  suitable 
for  refining  cadmium,  and  obtained  some  excellent  results 
with  fluosilicate  of  cadmium,  and  H.  Mennicke  |  has  applied 
the  acid  to  refining  tin  and  obtained  good  results.  These 
views  are,  however,  probably  incorrect.  The  true  suitability 
of  an  acid  is  more  dependent  on  its  strength,  and  solubility 
of  its  salts,  than  on  other  things. 

Messrs.  Senn  and  Mennicke  would  probably  have  done 
equally  well  with  other  non-oxidizing  acids  having  an  equal 
strength  and  forming  salts  of  cadmium  and  tin  respectively, 
of  equal  solubility. 

Prof.  Ostwald  in  his  work  "  Outlines  of  General  Chem- 
istry," translated  by  Dr.  James  Walker,  New  York,  1890, 
page  360,  gives  a  valuable  table  and  makes  this  statement 
in  connection  with  it. 

"  The  fact  stated  by  Hittorf  that  the  power  of  reaction 
and  the  electrolytic  conductivity  are  always  concurrent 
properties,  speaks  at  once  in  favor  of  this  assumption.  [That 
the  strength  of  an  acid  is  a  definite  and  definable  character- 
istic proportional  to  its  dissociation.]  It  obtains  further 
support  from  the  circumstance  that  the  processes  of  electro- 
lytic conductivity  and  of  chemical  decomposition  both  de- 
pend on  the  molecules  under  consideration  falling  into 
smaller  sub-molecules;  without  this  decomposition  there  can 
neither  be  a  new  distribution  of  parts  as  in  chemical  reaction, 
nor  a  transport  of  electricity  attached  to  the  ions,  as  in  con- 
duction. 


*  Zeitschrift  fur  Electrochemie.     II  (1905),  229-245. 

t  Zeitschrift  fur  Electrochemie.     XII  (1905),  112,  136,  161,  180. 


ELECTROLYTES   FOR   LEAD   REFINING.  19 

"  But  the  most  decisive  and  telling  argument  for  the 
soundness  of  the  assumption  is  the  numerical  agreement  of 
the  values  for  the  chemical  activity  on  the  one  hand  and  the 
electric  conductivity  on  the  other.  The  numbers  on  pages 
354  and  356  for  the  rate  of  catalysis  of  methyl  acetate  and 
of  the  inversion  of  cane  sugar,  agree  so  closely  with  those 
representing  the  relative  electric  conductivity,  that  there 
cannot  exist  the  slightest  doubt  of  the  intimate  connection 
between  the  two  series. 

"  In  the  following  table  there  is  tabulated  under  I.  the 
electric  conductivity  of  normal  solutions  of  acids,  under  II. 
the  coefficients  of  velocity  for  the  catalysis  of  methyl  acetate, 
and  under  III.  the  coefficients  of  inversion  of  cane  sugar. 

TABLE  6. 


Acid. 

1.  Hydrochloric,  HC1  

I. 
100 

II. 
100 

III. 
100 

2.  Hydrobromic,  HBr. 

100  1 

98 

111 

3.  Nitric,  HNO3.  .  . 

99  6 

92 

100 

4.  Ethanesulphonic,  C2H5SO2OH.  .  .  . 
5.  Isethioniq,  C2H4OH  -SO2OH.  . 

79.9 

77  8 

98 
92* 

91 

92 

6.  Benzenesulphonic,  C6H5  -SO2OH.  . 
7.  Sulphuric,  H2SO4  

74.8 
65  1 

99 
73  9f 

104 
73  2 

8.  Formic,  H  -COOH.  .  .  . 

1  68 

1  31 

1  53 

9.  Acetic,  CH3  -COOH 

424 

345 

400 

10.  Monochloracetic,  CH2C1  -COOH  .  .  . 
11.  Dichloracetic,  CH12  -COOH  

4.90 
25.3 

4.30 
23.0 

4.84 
27  1 

12.  Trichloracetic,  CC13  -COOH  

62  3 

68.2 

75  4 

18.  Lactic,  C2H4OH  -COOH.  .  . 

1  04 

902 

1  07 

25.  Oxalic,  (COOH)2  . 

19  7 

17  6 

18  6 

29.  Tartaric,  C2H2(OH)(COOH)2  
32.  Citric,  C3H4OH(COOH)3  

2.28 
1  66 

2.30 
1.63 

1  73 

33    Phosphoric  PO(OH) 

7  27 

6  21 

34    Arsenic  AsO(OH) 

5  38 

4  81 

*  Should  be  .98    1  oe.    ,  _  ^      .,,    ,      . 

t  Should  be  54.7  /  aS  °n  page  354  °f  °stwald  S  b°°k' 


20 


LEAD   REFINING   BY   ELECTROLYSIS. 


We  are  especially  interested  in  the  strength  of  fluosilicic 
acid,  fluoboric  acid,  and  dithionic  acid,  as  well  as  some  of 
those  given  in  the  table. 

Mr.  R.  H.  Sherry  made  determinations  of  the  strength 
of  these  by  the  methyl-acetate  method  as  described  in  Ost- 
wald's  same  book,  page  352,  and  also  made  tests  on  HC1  and 
H2S04  as  a  check.  His  results  cannot  be  directly  added  to 
Ostwald's  table,  as  they  were  made  at  different  temperatures 
and  a  different  amount  of  methyl-acetate  was  used. 

He  used  normal  solutions  of  H2SiF6,  that  is,  containing 
7.2  gr.  H2SiF6-per  100  cc.;  normal  solution  of  dithionic 
acid,  8.3  grams  H2S206  per  100  cc.;  normal  sulphuric  acid 
4.9  grams  per  100  cc.;  normal  hydrochloric  acid  3.65  grams 
HC1  per  100  cc.  Through  an  error  If  N  fluoboric  acid  was 
used  instead  of  normal,  and  the  only  basis  of  comparison 
made  was  with  1§N  HC1.  Normal  fluoboric  acid  =  8.8  grams 
BHF4  per  100  cc. 

.The  figures  give  the  amount  of  acetic  acid  liberated  in 
grams  in  90  minutes  and  are  very  nearly  proportional  to 
the  strength  of  the  acids. 


TABLE  7. 


At  Approximately  26°  C. 

At  26.5-27°  C. 

N  H2SO4 

(a)    .2330 

(6)     .2387 

N  H2SiF6 

NHC1 

NH2S,Oe 

1§N  HC1 

If  N  BHF4 

(a)    .2540 

(6)     .2578 

(a)    .4106 
(6)     .4116 

(a)    .4223 
(6)     .4169 

(a)     .5541 
(6)     .  5568 

(a)     .5450 
(6)     .5391 

We  then  get   approximately  the  ratios  of  the   following 
table,  taking  normal  HC1=100: 


ELECTROLYTES  FOR  LEAD  REFINING.         21 


TABLE  8. 

1.  Hydrochloric  acid,  HC1 100 

2.  Dithionic  acid,  H2S2O6 102 

3.  Fluboric  acid,  BHF4 95 

4.  Fluosilicic  acid,  H2SiF6 62 

5.  Sulphuric  acid,  HJ^ 57 

6.  Acetic  acid,  HCH3CO2 345 

7.  Ethyl  sulphuric,  C2H5SO4H 74 

8.  Benzene  sulphonic,  C6H5SO3H 74 


In  other  tables  in  his  book  Professor  Ostwald  gives  the 
strength  of  benzene-sulphonic  acid  and  ethyl  sulphuric  acid, 
as  determined  by  the  methyl  acetate  method,  as  practically 
100.  The  figures  in  this  table  are  for  determinations  made 
by  the  electric  conductivity  method.  I  do  not  think  the 
methyl  acetate  method  is  reliable  for  acids  having  an  organic 
residue  on  account  of  the  naturally  greater  dissolving  power 
such  acids  must  possess  even  in  solution,  for  organic  sub- 
stances as  methyl  acetate.  Such  determinations  certainly 
do  not  check  anyway  with  the  conductivity  determina- 
tions. 

In  recent  experiments,  all  these  strong  acids  have  been  made 
up  into  lead-depositing  electrolytes  containing  4  grams  and 
more  of  lead  per  100  cc.  beside  free  acid,  giving  lead  deposits 
of  varying  characteristics,  but  all  of  them  always  loose  and 
crystalline  and  unsuitable  for  practical  work,  on  account  of 
their  lack  of  solidity  and  the  short  circuits  produced.  All 
the  electrolytes  in  the  following  list  and  many  others,  too, 
have  produced  loose  deposits  without  exception. 

A  partial  list  of  electrolytes  used  for  depositing  lead  is 
given  in  Table  9,  the  figures  being  for  grams  per  litre. 


22  LEAD   REFINING   BY   ELECTROLYSIS. 

TABLE  9. 

400  grs.  lead  nitrate 

60  grs.  lead  nitrate,  33  grs.  sodium  nitrate,  6  grs.  nitric  acid 

250  grs.  lead  nitrate,  35  grs.  sodium  nitrate,  6  grs.  nitric  acid 

350  grs.  lead  nitrate,  35  grs.  sodium  nitrate,  6  grs.  nitric  acid 

33  grs.  lead  nitrate,  33  grs.  sodium  nitrate,  6  grs.  nitric  acid 

33  grs.  lead  nitrate,         100  grs.  sodium  nitrate,  6  grs.  nitric  acid 

100  grs.  lead  nitrate,         400  grs.  sodium  nitrate,  6  grs.  nitric  acid 

530  grs.  lead  acetate,         117  grs.  ammonium  acetate,  33  grs.  acetic  acid. 

1 400  grs.  sodium  nitrate  satuarted  with  lead  hydrate 

5.6  grs.  caustic  potash  saturated  with  lead  hydrate 

448  grs.  caustic  potash  saturated  with  lead  hydrate 

50  grs.  lead,     87  grs.,  BF4 

50  grs.  lead,  157  grs.  benzene  sulphonic  acid  radicle 

50  grs.  lead,  125  grs.  ethyl  sulphuric  acid  radicle 

27  grs.  lead  formate,  46  grs.  formic  acid 

60  grs.  lead  acetate,  60  grs.  acetic  acid 

32.5  grs.  lead  acetate,  60  grs.  acetic  acid,  60  grs.  potassium  acetate. 

186  grs.  lead  lactate,  93  grs.  lactic  acid 

186  grs.  lead  lactate,  186  grs.  lactic  acid 

With  the  addition  of  gelatine  to  the  strong  acid  solu- 
tions (fluosilicic,  fluoboric,  dithionic,  organic  sulphuric  and 
sulphonic  acids),  they  give  solid  lead  deposits,  the  best  of 
which  have  been  obtained  with  fluosilicic  and  fluoboric  acids, 
and  on  one  occasion,  when  the  solution  happened  to  be  in 
just  the  right  condition,  with  dithionic  acid.  Benzene-sul- 
phonic  acid  gives  the  roughest  deposits  and  is  the  most 
troublesome  to  use.  The  lead  salt  is  not  very  soluble. 

A  number  of  these  deposits  of  considerable  thickness  have 
been  examined  for  specific  gravity  from  time  to  time,  with 
these  results: 

TABLE  10. 

Fluosilicate 11.29  11.35  11.36 

Benzenesulphonate. 11 . 35  11 . 37 

Ethyl  sulphate 11 .27  11 .31 

Fluoborate 11 .39 

Dithionate 11 .20 

Phenolsulphonate 11 . 35 


ELECTROLYTES  FOR  LEAD   REFINING.  23 

Phenol-sulphonic  acid  gives  an  excellent  lead  deposit,  as 
does  benzene  disulphonic  acid  and  phenol  disulphonic  acid. 
All  the  other  organic  sulphonic  acids  that  I  tried,  as  toluene 
and  naphthalene  sulphonic  acids,  give  altogether  too  insolu- 
ble lead  salts.  Methyl-  and  amyl-sulphuric  acid  are  prac- 
tically equivalent  to  ethyl-sulphuric  acid.  Ethane  disulphonic 
acid,  from  C2H4Br2  and  ammonium  sulphite  by  Strecker's 
reaction,  gave  too  insoluble  a  lead  salt.  COC12  and  a  sul- 
phite solution  did  not  give  the  expected  dioxy  methylene 
disulphonic  acid.  Calcium  carbide  and  concentrated  sul- 
phuric acid  gives  a  number  of  sulphonic  acids,  but  I  have, 
not  investigated  this  reaction  to  a  great  extent. 

With  tax-free  alcohol  there  is  a  slight  chance  of  economic- 
ally using  ethyl-sulphuric  acid.  The  reaction  between  alcohol 
and  sulphuric  acid  is 

C2H5OH  +  H2S04 = C2H5S04H + H20 

and  provides  a  relatively  cheap  acid  for  refining  lead.  Ethyl- 
sulphuric  acid  in  strong  solution  decomposes,  however,  again 
into  alcohol  and  sulphuric  acid.  I  accordingly  determined 
the  decomposition  rate  of  a  solution  I  had,  which  contained 
10  grams  lead  and  8.8  grams  free  C2H5S04H  per  100  cc. 
This  solution  deposited  about  .03  grams  lead  sulphate  per 
day,  at  about  25°  C.  This  corresponds  to  about  2.1  Ibs. 
C2H5S04H  decomposed  per  ton  lead  refined.  To  prepare 
2.1  Ibs.  of  the  acid  would  require  about  1  Ib.  alcohol  and  2 
Ibs.  fuming  H2S04  (30%  S08).  The  alcohol  would  cost  at 
least  4  cents  and  the  sulphuric  acid  2.5  cents,  or  a  total 
cost  per  ton  lead  for  these  materials  of  6.5  to,  say,  10  cents. 
The  above  solution  was  pretty  weak,  however,  and  the  tern- 


24  LEAD   REFINING   BY   ELECTROLYSIS. 

perature  a  little  low,  so  I  think  it  would  be  found  with  such 
a  solution  as  would  be  used  practically,  that  the  decompo- 
sition would  be  three  or  more  times  as  great.  The  resistance 
of  this  solution  of  lead  ethyl  sulphate  and  ethyl  sulphuric 
acid  (10  grams  lead  and  8.8  grams  C2H5S04H  per  100  cc.) 
was  at  27°  C.,  2.6  ohms  per  cubic  inch  as  against  about  1.4 
ohms  for  the  regular  fluosilicate  solutions. 

Solutions  of  lead  phenol-sulphonate  gave  excellent  re- 
sults as  far  as  conductivity  and  solid  lead  deposition  went, 
but  the  solution  seemed  to  be  unstable  for  a  crystalline 
deposit  kept  forming  for  a  long  time.  The  sulphonation  of 
the  phenol  takes  place  readily  and  good  yields  may  be  ob- 
tained. 20  grams  of  phenol  were  heated  up  to  180°  C.  for 
one  hour  with  varying  quantities  of  H2S04.  With  25  grams 
H2S04,  titration  of  the  product  with  sodium  carbonate, 
showed  that  the  reaction  was  nearly  quantitative.  With 
more  sulphuric  acid,  considerable  disulphonic  acid  was 
obtained,  about  30%  of  the  monosulphonic  acid  being  con- 
verted to  disulpho-acid,  when  40  grams  £[2864  were  used  for 
20  grams  phenol. 

A  solution  containing  75%  mono-acid  and  25%  di-acid 
and  30  grams  lead  in  100  cc.,  of  the  following  composition: 
lead  30  gr.,  C6H5S03'  28.4  gr.,  and  C6H4(S03)2//  15.2  gr.  per 
100  cc.  gave  a  resistance  per  cubic  inch  of  2.04  ohms. 

The  solution  was  practically  neutral  and  the  resistance 
would  no  doubt  have  been  much  less  with  more  free  acid. 
However,  the  relatively  high  cost  of  pure  phenol,  and  the 
difficulty  I  found  in  trying  to  get  a  suitable  solution  from 
crude  phenol  or  cresol,  led  to  the  abandonment  of  these  ex- 
periments, although  they  looked  promising  at  first. 

Lead    benzene-sulphonate   is   relatively   little   soluble   and 


ELECTROLYTES   FOR   LEAD   REFINING.  25 

the  lead  deposit  was  poor.     It  is  also  more  difficult  to  get 
even  a  fair  yield  of  benzene  sulphonic  acid. 

Many  tests  have  been  made  with  dithionic  acid  electro- 
lytes, and  on  one  occasion  a  very  excellent  deposit  was  got. 
All  the  other  experiments  have  given  a  rather  poor  deposit. 
The  surpassing  conductivity  of  dithionic  acid,  the  fact  that 
the  only  raw  material  actually  necessary  to  make  it  is  SO  2 
which  so  many  works  have  plenty  of  and  to  spare,  make  it 
seem  almost  an  ideal  electrolyte.  The  acid  is  subject  to 
decomposition,  however,  in  strong  or  warm  solution,  as  fol- 
lows: 


both  the  products  of  reaction  being  bad.  The  sulphuric  acid 
precipitates  lead  sulphate  into  slime,  but  worst  of  all,  the  S02 
is  reduced  by  the  cathode,  forming  lead  sulphide. 

S02  +  3Pb  +  2H2S206  -  2PbS206  +  2H20  +  PbS, 

which  spoils  the  cathode  deposit,  if  deposited  in  any  quan- 
tity. The  one  good  deposit  I  mentioned  probably  resulted 
from  the  use  of  a  solution  freshly  made  up  with  crystallized 
lead  dithionate,  water,  and  dilute  sulphuric  acid  to  precipi- 
tate out  part  of  the  lead  and  set  free  some  of  the  dithionic 
acid,  which  contained  no  S02. 

I  had  experiments  made  lasting  for  several  week's  con- 
tinuous run  with  another  solution,  but  the  deposit  was  "  door- 
mat" to  the  last,  but  I  am  not  satisfied  that  the  solution,  if 
used  properly,  cannot  be  made  to  yield  an  excellent  deposit.* 


*  Since  the  above  was  written  further  experiments  have  also  failed  to 
give  an  entirely  satisfactory  deposit  continuously. 


26  LEAD   REFINING   BY   ELECTROLYSIS. 

The  rate  of  decomposition  is  quite  slow.  A  solution  con- 
taining 6.6  grams  Pb  and  5.75  grams  free  H2S206,  or  a  total 
of  10.75  grams  S206  per  100  cc.,  giving  a  resistance  per 
cubic  inch  at  26.5°  C.  of  1.92  ohms  (a  fluosilicate  solution 
of  corresponding  acidity  would  be  about  2.6-2.7  ohms),  de- 
composes at  the  rate  of  complete  decomposition  of  the  S206 
in  about  80  weeks,  or  from  1.75  to  2.2  Ibs.  H2S206  decom- 
posed per  ton  of  lead  refined.  Another  solution  containing 
7.5  grams  lead  and  14.4  grams  S20e  per  100  cc.,  decomposed 
in  5J  months  at  the  rate  of  total  decomposition  in  36  years. 
The  conductivity  of  a  solution  containing  7.5  grams  Pb  and 
12.6  grams  S206"  per  100  cc.  at  21J0  was  1.75  ohms. 

The  preparation  of  the  dithionic  acid  we  used  was  accom- 
plished in  two  different  ways.  In  each  case  Mn02  was  dis- 
solved in  water  by  a  current  of  S02  gas  passed  through.  Two 
reactions  may  take  place  as  follows,  of  which  the  first  is  the 
only  useful  one: 


Mn02+  S02  =  MnS04. 

Conditions  favoring  the  first  are  low  temperature,  say 
10°  C.,  and  the  continual  presence  in  the  solution  of  an  excess 
of  S02.  Under  these  favorable  conditions  the  yield  has  been 
as  high  as  86%  of  the  manganese  dissolved  converted  to 
dithionate  and  14%  to  sulphate,  or  a  yield  of  93%  on  the  S02 
used.  In  another  case  the  yield  on  sulphur  was  81.6%,  and 
on  manganese  dissolved  63.3%.  The  reaction  between  the 
manganese  dioxide  and  H2S03  is  rapid. 

At  first  the  manganese  salt  was  decomposed  with  lead 
peroxide:  MnS206+Pb02  =  Mn02+PbS206.  It  was  soon 


ELECTROLYTES   FOR   LEAD   REFINING.  27 

found  that  while  this  reaction  was  all  right  when  sulphates 
were  absent  from  the  solution,  the  yield  was  poor  otherwise. 
We  accordingly  precipitated  the  S04  first  by  adding  lead 
dithionate  from  a  previous  batch.  It  was  thought  that  the 
manganese  dioxide  precipitate  could  be  used  over  and  over 
again,  but  the  precipitated  dioxide  will  not  give  nearly  as 
good  a  yield  as  native  pyrolusite. 

Only  certain  varieties  of  lead  peroxide  will  react  with  the 
lead  solution.  The  peroxide  precipitated  by  heating  a  mixed 
solution  of  lead  acetate  and  calcium  hypochlorite,  did  very 
well,  but  the  cost  would  be  too  high  for  practical  work,  so 
I  devised  an  electrolytic  method  as  follows:  By  electrolyzing 
a  solution  of  common  salt  with  carbon  cathode  and  lead 
anode,  lead  hydrate  is  precipitated,  especially  well  if  the  solu- 
tion is  heated  a  little.  If  the  mixture  is  then  electrolyzed 
with  carbon  anode  and  lead  cathode,  sodium  hypochlorite 
is  produced,  which  converts  the  lead  hydrate  into  lead  peroxide. 
The  original  idea  was  to  merely  reverse  the  current  occa- 
sionally, but  that  did  not  do  very  well  because  there  was 
always  a  coating  on  the  lead  anode,  and  when  the  current 
was  reversed  the  coating  was  again  reduced  to  spongy  lead 
with  a  corresponding  loss  of  efficiency.  The  difficulty  was 
surmounted  by  using  two  sets  of  electrodes  in  different  parts 
of  the  cell,  and  even  then  there  was  difficulty  with  the  for- 
mation of  a  coating  on  one  of  the  electrodes,  but  an  obser- 
vation of  Dr.  Kern  that  the  coatings  fell  off  if  the  current 
was  interrupted  entirely  for  a  short  time  occasionally,  put 
us  in  possession  of  a  practicable  process  of  preparing  the  pre- 
cipitated lead  peroxide  from  lead  anodes  by  the  help  of  elec- 
tricity. The  product  was  entirely  free  from  Pb(OH)2  if  the 
proportion  of  the  two  sets  of  reactions  we  were  carrying  on 


28  LEAD   REFINING   BY   ELECTROLYSIS. 

were  so  adjusted  that  there  was  always  excess  of  NaOCl 
formed. 

The  other  method  of  preparation  is  based  on  treating  the 
manganese  dithionate  and  sulphate  solution  with  slacked 
lime,  giving  a  solution  of  the  calcium  salt,  and  a  precipitate 
containing  the  manganese,  which  could  perhaps  be  used 
equally  as  well  or  better  than  the  original  Mn02  ore  used, 
in  a  Spiegeleisen  or  ferromanganese  furnace,  thus  paying  for 
the  manganese.  The  calcium  salt  was  decomposed  with  sul- 
phuric acid  for  calcium  sulphate  and  dithionic  acid.  I  had 
experiments  made  in  my  laboratory  on  this  process,  but  the 
results  do  not  show  anything  for  or  against  its  probable 
success. 

Fluoboric  acid  is  a  somewhat  better  conductor  than  fluo- 
silicic  acid,  if  the  comparison  is  made  on  the  basis  of  equal 
neutralizing  power,  in  about  the  ratio  3  to  2  for  weak  solu- 
tions, the  difference  becoming  less  as  the  solutions  become 
stronger.  The  amount  of  HF  required  to  produce  the  acids 
in  the  ratio  for  equal  acidity,  is  80  to  61.  For  weak  solutions 
for  a  given  amount  of  fluorine,  a  slightly  greater  conduc- 
tivity can  be  secured  by  the  use  of  boric  instead  of  silicic 
acid. 

For  the  relatively  stronger  acids  that  must  be  used  for 
economical  reasons,  the  advantage  is  with  fluosilicic  acid, 
both  in  amount  of  HF  required  and  in  cost  of  silicic  acid  as 
against  boric  acid.  Thus  a  solution  containing  5  gr.  Pb  and 
15  gr.  BF4'  per  100  cc.  has  a  resistance  at  30°  C.  of  about 
1.4  ohms,  and  a  solution  with  5  gr.  Pb  and  16.3  gr.  SiF6" 
per  100  cc.  (each  containing  13.1  gr.  F)  has  a  resistance  of 
about  1.3  ohm,  per  inch  X  inch2  unit. 

Considering  the   higher   cost   of   boric   acid   used   as   raw 


ELECTROLYTES    FOR   LEAD   REFINING.  29 

material,  these  figures  lead  to  the  conclusion  that  fluosilicic 
acid  is  considerably  the  best. 

Fluosilicic  acid  is  soluble  in  water  and  decomposable  by 
alkalies  into  alkali  fluoride  and  silica.  Even  as  weak  a  base 
as  litharge  will  effect  a  decomposition,  which  is  the  reason 
white  lead  and  not  litharge  is  used  in  making  the  lead  salt. 
Heating  causes  a  loss  of  acid  by  volatilization  if  the  acid  is 
strong. 

According  to  Baur,*  Stolba  noticed  in  1863  that  if  fluo- 
silicic acid  is  boiled  down  the  residue  will  dissolve  silica, 
therefore  SiF4  must  have  escaped  in  boiling.  The  author 
(Baur)  has  found  it  to  be  the  case  that  an  acid  containing 
13.3%  H2SiF6  gives  a  distillate  also  containing  H2SiF6. 
Weaker  acids  give  distillates  with  excess  of  HF,  stronger  acids 
with  excess  of  SiF4.  If  then  concentrated  H2SiF6  is  dis- 
tilled partly,  without  silica  being  present,  the  residue  should 
be  caapble  of  dissolving  silica;  if  weak  acids  5-10%  are 
evaporated,  silica  should  deposit.  This  is  found  by  experi- 
ment to  be  the  case.  The  relative  amounts  of  steam  and 
hydrogen  and  silicon  fluorides  escaping  are  not  given  by  the 
author. 

The  specific  gravity  of  fluosilicic  acids  is  given  in 
Table  11,  taken  from  Comey's  "  Dictionary  of  Solubilities," 
originally  given  by  Stolba. 

The  preparation  of  lead  fluosilicate  solution  from  fluo- 
silicic acid  can  be  successfully  carried  out  in  at  least  two 
ways.  The  most  convenient  method  is  to  add  lead  carbon- 
ate or  white  lead,  which  dissolves  with  effervescence. 


*  Berichte,  Deutsch.  Chem.  Ges.  1903.     36    (16),  4209,  abstracted   Jour. 
Soc.  Chem.,  Vol.  27,  page  17. 


LEAD    REFINING   BY   ELECTROLYSIS. 


TABLE   11. 


Per  Cent  H2SiFe 

Specific  Gravity. 

Per  Cent  H2SiF6 

Specific  Gravity. 

2 

1.0161 

20 

.1748 

4 

.0324 

22 

.1941 

6 

.0491 

24 

.2136 

8 

.0661 

26 

.2335 

10 

.0834 

28 

.2537 

12 

.1011 

30 

.2742 

14 

.1190 

32 

1.2951 

16 

.1373 

34 

1.3162 

18 

.1559 

In  his  paper  Mr.  Senn  *  describes  an  experiment  in 
which  he  added  to  100  grams  of  19.2%  H2SiF6,  100  grams 
of  lead  as  white  lead,  and  got  a  precipitate  containing"  83.3% 
PbF2  and  16.68%  Si02.  This  is  of  course  the  result  when  a 
great  excess  of  lead  is  used,  which  is  not,  however,  a  matter 
of  practical  importance.  Practically  in  making  lead  fluo- 
silicate  solution,  little  or  no  precipitate  is  formed. 

Perhaps  a  cheaper  method,  though  a  less  convenient  one, 
is  to  electrolyze  the  solution  with  lead  anode  and  cathode, 
separated  by  a  diaphragm.  I  made  up  about  10  cubic  feet 
of  solution  experimentally,  in  fact  this  .was  the  first  method 
used.  The  solution  was  brighter  and  whiter  and  gave  a  bet- 
ter deposit  on  the  start  than  that  made  in  the  other  way. 
It  also  happened  to  contain  an  excess  of  HF.  The  solution 
was  stored  in  carboys,  and  it  finally  dissolved  the  glass  and 
ran  out.  Yet  the  excess  of  HF  did  not  cause  any  precipi- 
tation of  PbF2  when  the  solution  was  used  in  refining. 

In  using  this  method,  the  lead  anodes  dissolved  evenly, 
the  e.m.f.  of  the  cell  was  about  li  volts,  and  no  precipita- 


*  Zeitschrift  fur  Elektrochemie,  April  14,  1905. 


ELECTROLYTES  FOR  LEAD  REFINING. 


31 


tion  was  formed.  A  very  little  black  spongy  lead  deposited 
on  the  cathodes,  with  much  hydrogen.  That  the  HF  present 
did  not  precipitate  lead  fluoride,  is  due  to  the  fact  that  HF 
is  relatively  a  weaker  acid  than  H2SiF6,  and  PbF2  is  not 
entirely  an  insoluble  salt.  The  saving  made  by  using  lead 
as  raw  material  instead  of  white  lead,  and  apparatus  to  be 
used,  are  treated  on  pages  243  and  244.  The  apparatus  used 
in  making  the  solution  is  also  shown  in  Fig.  1. 


FIG.  \, 

The  crystallization  of  lead  fluosilicate  is  a  difficult  mat- 
ter. The  best  results  are  got  by  placing  a  strong,  nearly 
neutral  solution  over  sulphuric  acid  under  a  bell  jar  and  giving 
the  solution  several  weeks  to  concentrate  and  crystallize,  when 
beautiful  crystals  are  obtained.  The  evaporation  of  the  solu- 
tion even  at  40-50°  C.  causes  the  precipitation  of  a  fine  crys- 
talline product  of  inexact  composition,  not  entirely  soluble 
in  water.  Crystals  have  also  been  got  by  dissolving  lead 


32  LEAD   REFINING   BY   ELECTROLYSIS. 

and  lead  peroxide  in  very  strong  fluosilicic  acid  and  lead 
fluosilicate  solutions,  from  two  electrodes  connected  together 
through  a  resistance. 

Lead-fluosilicate  crystallizes  in  very  soluble,  brilliant  crys- 
tals, resembling  those  of  lead-nitrate,  and  containing  four 
molecules  of  water  of  crystallization,  with  the  formula 
PbSiF6-4H20.  This  salt  dissolves  at  15°  C.  in  28  per  cent 
of  its  weight  of  water,  making  a  syrupy  solution  of  2.38  sp. 
gr.  Heated  to  60°  C.,  it  melts  in  its  water  of  crystallization* 
A  neutral  solution  of  lead-fluosilicate  is  partially  decomposed 
on  heating,  with  formation  of  a  basic  insoluble  salt  and  free 
fluosilicic  acid,  which  keeps  the  rest  of  the  salt  in  solution. 

The  electrolysis  of  fluosilicic  acid  and  probably  also  of 
fluosilicates,  is  not  entirely  a  simple  electrolysis  in  which  the 
ions  H'  and  HSiF6'  take  part.  There  is  a  tendency  toward 
decomposition  into  Si02  and  6HF,  the  reverse  of  its  forma- 
tion. Late  experiments  indicate  that  this  takes  place  to  some 
considerable  extent,  but  for  the  most  part  the  HF  liberated 
at  the  cathode  and  the  silica  at  the  anode  recombine  under 
the  influence  of  circulation  and  diffusion.  An  excess  of  HF 
in  the  solution  would  obviously  tend  to  prevent  the  forma- 
tion of  silica,  and  a  solution  containing  excess  of  silica  would 
deposit  silica  in  the  anode  slime  until  a  condition  of  equilibrium 
was  arrived  at,  when  no  more  silica  would  deposit.  There 
is  a  certain  loss  of  fluosilicic  acid  in  actual  practice  which  I 
regard  is  mostly  due  to  mechanical  loss  by  leaks,  etc.,  because 
the  silica  in  the  slime  is  generally  about  2%  only,  or  about 


*  Belts   and    Kern,   Trans.   Am.    Electrochem.    Soc.,    Vol.    6,    page   67. 
Clarke,  Am.  Chem.  Soc. 

f  F.  W.  Clarke,  Jr.,  Am.  Chem.  Soc.,  28,  306,  190. 
J  Private  communication  from  the  management. 


ELECTROLYTES   FOR  LEAD   REFINING.  33 

one  pound  per  ton  of  lead,  corresponding  to  2.3  pounds  of 
H2SiF6  decomposed.  Solution  has  been  thought  to  dissociate 
into  which  HF  evaporates  into  the  air,  while  the  corresponding 
silica  remains  in  the  slime.  The  actual  amount  of  HF  present 
in  the  solution  is  usually  slight,  and  its  evaporation  must  be 
very  small,  on  account  of  small  vapor  tension  and  high  com- 
bining power  with  water.  The  fumes  produced  in  a  closed 
tank-room,  refining  perhaps  70  tons  of  lead  daily,  on  the  sup- 
position that  the  acid  is  lost  in  the  air  to  the  extent  of  100 
to  300  or  more  Ibs.  fluorine  in  the  form  of  SiF4  and  HF  per. 
day,  would  make  the  air  unbearable,  whereas  the  actual  con- 
dition is  that  there  is  no  noticeable  acid  fume  in  the  air 
even  in  winter  with  the  building  closed.  I  cannot,  therefore, 
believe  that  appreciable  quantities  of  acid  are  lost  by  evap- 
oration from  the  tanks. 

There  is  always,  of  course,  a  considerable  mechanical  loss 
in  the  large  bulk  of  slime,  in  the  pores  of  the  cathodes,  and 
on  the  surface  of  both  cathode  and  anode  scrap,  and  from 
leaks  in  the  tanks.  New  tanks  absorb  some  solution  and 
the  salt  PbSiF6  probably  crystallizes  in  the  wood,  which  also 
causes  a  loss  with  new  tanks.  In  view  of  these  facts  and  also 
analyses  of  slime,  the  loss  of  acid  by  electrolytic  decompo- 
sition not  offset  by  the  reaction  between  the  Si02  and  HF 
formed  is  probably  extremely  small. 

That  silica  deposits  on  anodes  from  solutions  containing 
fluosilicic  acid  has  been  proved  by  electrolyzing  solutions  of 
ferric  sulphate  containing  fluosilicic  acids  and  analyzing  the 
slimy  coating  on  the  anode  in  a  similar  experiment,  and  by 
the  electrolysis  of  ferrous  fluosilicate;*  in  both  cases  with  an 
insoluble  carbon  anode. 

*  Private  communication.     Aug.  E.  Knorr. 


34  LEAD    REFINING   BY   ELECTROLYSIS. 

In  either  case  silica  deposits  on  the  anode,  whereas  if 
H2SiF6  was  not  decomposable  in  solution  no  such  thing  would 
occur.  In  his  article  "  Zur  Kenntnis  der  Elektrolytischen 
Bleiraffination, "  H.  Senn  also  described  an  experiment  in 
which  he  electrolyzed  fluosilicic  acid  with  platinum  electrodes, 
when  silica  separated. 

"  EXPERIMENT  40. — I  used  as  electrolyte  fluosilicic  acid 
of  specific  gravity  1.267  (36.7  gr.  H2SiF6  per  100  cc.).  This 
contained  a  little  hydrofluoric  acid.  Electrodes:  platinum. 
Anode  surface:  36.8  sq.  cms.  Cathode  surface  41.6  sq.  cms. 
Current:  0.45  amperes.  Tension:  2.7  volts.  Time  19  hrs. 

"  At  the  close  of  the  research  the  anode  and  the  bottom 
of  the  glass  were  covered  with  a  layer  of  gelatinous  silica. 
The  electrolyte  had  the  peculiar  smell  of  hydrofluoric  acid. 
This  had  attacked  the  glass.  Since  I  had  no  method  of 
determining  hydrofluoric  acid  in  presence  of  fluosilicic  acid, 
I  had  to  be  content  with  a  qualitative  proof. 

"  The  fluosilicic  acid  I  filtered  off  and  found  in  250  cc. 
of  electrolyte  .1841  grams  Si02,  corresponding  to  .4401  grams 
H2SiF6.  This  decomposition  is  indeed  a  result  of  the  fact 
that  SiF6  was  discharged  on  the  anode." 

That  the  silica  should  deposit  on  the  anode  rather  than 
on  the  cathode  is  a  little  surprising  at  first.  If  there  is  a 
dissociation  of  H2SiF6  into  HF  and  Si02,  as  some  have  thought, 
HF  is  so  much  more  a  conductor  than  Si02  that  it  would 
apparently  go  to  the  anode  to  a  greater  extent  than  Si02, 
and  at  the  anode  there  would  be  an  excess  of  HF,  not  Si02. 

In  the  experiment  of  Senn's  the  proportion  of  silica  de- 
posited corresponds  to  a  decomposition  of  0.48%  of  all  the 
H2SiF6  present,  and  as  the  glass  was  attacked,  some  or  all 
of  this  must  have  come  from  the  glass.  In  this  experiment 


ELECTROLYTES   FOR   LEAD   REFINING.  35 

there  may  have  been  a  good  deal  more  decomposition  than 
this,  as  the  continual  circulation  would  bring  the  anode  and 
cathode  products  together  again,  when  the  original  equilib- 
rium from  formation  of  H2SiF6  would  be  again  established. 

The  maximum  chemical  and  mechanical  loss  cannot  be 
more  than  6  Ibs.  of  H2SiF6  per  ton  of  lead  deposited,  for 
analyses  of  a  solution,  thoroughly  mixed  both  before  and 
after  a  certain  150  tons  of  lead  was  deposited  with  a  current 
density  of  10-12  amperes  per  square  foot,  showed  only  this 
amount  of  loss.  The  solution  contained  15%  SiFe  and  about 
6%  Pb,  Any  greater  loss  than  this,  observed  \vhen  working 
at  this  current  density,  must  then  be  an  avoidable  mechanical 
loss,  as  indeed  part  of  this  6  Ibs.  loss  must  have  been. 

A  sample  of  Trail  slime  from  regular  running,  analyzed 
by  me,  contained  2.2%  Si02  including  silica  in  H2SiF6  present. 
The  slime  of  course  is  not  completely  washed  over,  and  part 
or  all  of  this  silica  then  is  due  to  the  electrolyte  not  washed 
out.  This  shows  a  maximum  loss  in  slime  of  about  2.1  Ibs. 
H2SiFe  per  ton  lead,  occurring  at  the  time  that  particular 
slime  was  made.  Even  part  of  the  apparent  loss  is  in  some 
cases  the  result  of  deposition  of  excess  of  silica  present 
in  the  solution  used. 

Solutions  of  fluosilicic  acid  may  contain  excess  of  silica, 
and  it  is  probable  that  H2SiOF4  is  formed  to  at  least  a  slight 
extent,  while  after  in  use  some  time  they  probably  contain 
excess  of  HF.  In  all  cases  the  amount  of  the  unstable  com- 
pounds in  solution  will  vary  with  the  concentration,  tem- 
perature, etc.  For  that  reason  I  think  determinations  of 
silica  in  anode  residues  from  lead  refined  with  new  solutions 
are  not  reliable  as  indicating  the  extent  to  which  H2SiF6  is 
decomposed,  nor  what  a  lead  fluosilicate  solution  will  do  after 


1 

36  LEAD   REFINING   BY   ELECTROLYSIS. 

it  has  practically  reached  its  condition  of  equilibrium.  H. 
Senn  gives  a  few  illuminating  analyses  in  his  paper  which 
show  the  point  I  am  making. 

TABLE   12. 

Experiment  Number.  SiOs  in  Slime. 

28  24.87% 

30  25.12% 

34  1.82% 

35  1.26% 

36  .9% 

It  will  be  noted  that  the  large  proportion  of  Si02  was 
found  in  slime  from  new  solution. 

Starting  with  a  solution  which  will  deposit  silica  in  the 
slime,  while  the  ratio  of  Si  to  F  in  the  solution  gradually 
becomes  less,  ultimately  a  condition  of  equilibrium  will  be 
reached  for  any  given  constant  conditions  of  temperature,: 
current  density,  strength  of  solution,  etc. 

Just  at  what  point  equilibrium  will  be  reached,  that  is 
when  the  power  of  the  solution  containing  free  HForH2SiF6, 
capable  of  combining  with  silica  to  form  H2SiF40  or  H2SiF6, 
is  exactly  balanced  by  the  tendency  of  the  current  to  deposit 
silica  on  the  anodes  is  impossible  to  say,  and  on  account  of 
the  constantly  varying  conditions  it  is  not  apt  to  be  deter- 
mined. 

However,  equilibrium  will  be  reached  long  before  the  solu- 
tion can  contain  so  much  free  HF  that  PbF2  can  precipitate 
or  other  undesired  reactions  occur.  With  an  ordinary  solu- 
tion, say  7  grams  Pb  and  16  grams  SiF6  per  100  cc.  as  much 
as  5%  free  HF  may  be  present  without  precipitating  PbF2. 
That  is,  the  acidity  due  to  HF  may  be  as  high  as  that  due 
to  free  H2SiF6  without  precipitating  PbF2,  of  course  on 
account  of  the  fact  that  H2SiF6  is  relatively  a  much  stronger 


ELECTROLYTES    FOR   LEAD   REFINING.  37 

acid  than  HF,  and  is  able  to  decompose  a  limited  amount 
of  insoluble  PbF2. 

Evidently  if  a  start  is  made  with  a  particular  solution, 
the  slime  may  very  easily  contain  a  good  deal  of  silica  on  the 
start,  until  equilibrium  is  reached,  but  this  does  not  mean 
a  loss  of  valuable  fluorine,  but  of  relatively  valueless  silica. 
On  the  other  hand,  by  having  a  certain  amount  of  free  HF 
present,  the  slime  can  contain  no  precipitated  silica.  In 
practice  very  high  silica  in  the  slime,  say  15%,  is  apt  to  be 
obtained  on  the  start  with  a  new  solution. 

Evidently  the  surface  of  the  cathodes,  anode  scrap,  and 
metal  particles  of  the  slime  that  must  be  taken  from  the 
solution  and  wetted  by  it,  is  quite  large.  On  account  of  the 
ease  with  which  slime  can  be  broken  up  and  washed,  the  loss 
in  the  slime  can  be  reduced  to  almost  any  extent.  The  sur- 
face of  the  anode  scrap  and  cathodes  can  also  be  freed  from 
acid  to  any  extent  by  washing,  but  if  there  are  any  pockets 
of  solution  in  the  cathodes,  or  any  chemical  combination  of 
lead  with  the  electrolyte,  as  in  copper  deposited  from  the 
acetate  solution  under  certain  conditions,*  such  losses  would 
be  unavoidable. 

To  investigate  the  losses  practically  resulting  from  elec- 
trolyte carried  off  by  the  cathodes,  six  pieces  of  cathodes  from 
a  large  pile  were  obtained  from  the  United  States  Metals 
Refining  Company's  Grasselli  plant,  and  analyzed  as  follows: 
Samples  of  100-150  grams  were  dissolved  slowly  while  warm- 
ing only  slightly  in  dilute  nitric  acid,  of  which  only  a  rather 
small  excess  was  used.  A  very  little  water-glass  solution 
was  added  to  the  dilute  acid  on  the  start,  to  insure  that  the 


*  "Ueber  das  Acetatkupfer. "     Carl  Benedicks.     Metallurgie,  1907  (4)  5. 


38 


LEAD    REFINING   BY   ELECTROLYSIS. 


fluorine  present  would  be  combined  as  SiF6.  The  water-glass 
dissolved  entirely,  but  during  the  solution  of  the  lead  some 
silica  separated.  This  was  filtered  off,  the  free  nitric  acid 
nearly  neutralized  with  caustic  potash  (by  alcohol)  and  a 
large  excess  of  potassium  nitrate  and  acetate  added.  The 


45  6 

PLATE  1. — SAMPLES  OF  LEAD  CATHODES. 

precipitated  K2SiF6  was  filtered  off  and  titrated,  giving  the 
following  results.  The  photographs  show  the  lead  pieces  from 
which  the  samples  were  cut,  one  photograph  showing  one 
side  and  the  other  photograph  the  other  side. 


TABLE   13. 


Number  in 
Photograph. 

1 015%  SiFe 

2 011%  " 

3 005%  " 

4 009%  " 

5 002%  " 

6 003%  " 


0 . 30  Ib.  SiF6  per  ton  lead. 

0.22  ' 

0.10  ' 

0.18  ' 

0.04  ' 

0.06  ' 


ELECTROLYTES  FOR  LEAD  REFINING. 


39 


We  have  evidently  a  very  small  loss  of  acid  in  the  cathodes, 
and  I  have  been  informed  that  results  similar  to  mine  have 
been  obtained  at  the  Trail  refinery.* 

The  method  of  washing  cathodes  in  use  when  the  above 
pieces  were  made  was  to  wash  them  with  water  first,  and  use 

1  2  3 


45  6 

PLATE  2  — SAMPLES  OF  LEAD  CATHODES. 

the  wash- water  over  and  over  until  nearly  of  the  same  strength 
as  the  main  electrolyte,  when  the  wash-water  is  added  to 
the  electrolytic  tanks.  The  average  loss  from  acid  solution 
remaining  on  the  cathodes  after  draining  is  evidently  about 
one-half  the  loss  involved  if  the  electrolyte  was  merely  allowed 
to  drain  off.  To  determine  just  what  this  loss  might  be, 
samples  2,  4,  5,  and  6  in  the  photographs,  were  cleaned  of 
a  surface  coating  of  white  lead,  and  weighed  after  wetting 
and  draining  for  a  minute  or  two,  and  again  after  becoming 
dry,  with  the  result  given  in  Table  14. 

*  Letter  from  Mr.  W.  H.  Aldridge. 


40  LEAD   REFINING    BY    ELECTROLYSIS. 

TABLE   14. 


Number  in 
Photo- 
graph. 

Weight  Cath- 
ode per 
Square  Foot. 

Solution  on 
Cathode. 

Acid  Loss 
per  Ton 
Lead. 

Average 
Loss  in 
Practice. 

Remarks  . 

2 

28.8  Ibs. 

0.50% 

1.66  Ibs. 
SiF6 

0.83  Ibs. 

SiF6 

Cathode  average 
weight  and 
roughness. 

4 

22       Ibs. 

0.39% 

1.33  Ibs. 

SiFti 

0.67  Ibs. 

SiF6 

Cathode  average 
weight  and 
roughness. 

5 

16       Ibs. 

0.36% 

1.20  Ibs. 

SiF6 

0.60  Ibs. 

SiFc 

Unusual  cathode. 

6 

11       Ibs. 

0.22% 

0.76  Ibs. 

SiF6 

0.38  Ibs. 

SiF6 

Unusual  cathode 
not  well  wetted. 

The  above  cathodes  were  deposited  from  a  solution  con- 
taining 8%  Pb,  and  are  solider  than  those  obtained  with  a 
.solution  containing  6%  Pb,  as  used  at  Trail,  which  may 
.account  somewhat  for  the  higher  acid  loss  at  Trail. 

The  maximum  loss,  with  fairly  solid  cathodes  of  average 
thickness,  of  28  to  30  Ibs.  per  square  foot,  is  not  greater  than 
1  Ib.  SiF6  per  ton  lead.  The  loss  on  anode  scrap  cannot  be 
over  30  to  40%  of  this  amount,  on  account  of  smaller  surface 
(1  anode  makes  2  cathodes  usually)  and  smoother  surface  both. 

The  loss  in  slime  may  be  reduced  by  a  moderate  amount 
of  washing  to  2  Ibs.  SiF6  per  ton  lead  or  lower.  The  loss  out- 
side of  leaks,  which  can  of  course  vary  extremely,  and  evap- 
oration from  the  tanks  which  cannot  be  otherwise  than  neg- 
ligible, when  the  air  in  the  tank-room  has  no  acid  smell,  as 
is  usually  the  case,  cannot  then  be  over  3.5  Ibs.  SiF6  per  ton. 
If  more  than  this,  something  is  wrong  with  the  plant,  which 
might  be  due  to  a  bad  leak  or  not  sufficient  washing  of  the 
slime,  or  deposition  of  soft  rotten  lead  on  the  cathodes  or 
other  less  evident  causes. 


ELECTROLYTES   FOR   LEAD   REFINING.  41 

The  acid  loss  at  Trail  in  1902  and  early  in  1903  was  as 
given  in  Table  15. 

TABLE   15. 

Aug.  3 — Sept.  16,         245      tons  deposited     13.8  Ibs.  SiF6  per  ton  deposited. 
Sept.  16— Oct.  6,          120         "  "  7.7    "      "      "     " 

Jan.  22— Feb.  13,     135-145     "  "  6.3    "      "      "     " 

The  solution  was,  however,  weaker  than  is  used  at  present, 
as  follows: 

TABLE   16 

Aug.  3,  7.86%  Pb  10.58%  SiFG 

Sept.  16,  6.19%  M  7.94%  " 

Oct.    6,  6.07%  "  6.93%  " 

Jan.  17,  6.40%  "  8.56%  " 

On  the  other  hand  during  at  least  the  first  two  of  the 
above  periods,  no  evaporation  of  wash-water  was  practised, 
and  only  enough  was  used  in  a  crude  way  to  make  up  for 
the  solution  taken  out.  There  were  leaks,  too,  and  no  suit- 
able apparatus  for  catching  a  good  share  of  them. 

The  average  amperes  and  volts  at  the  time  may  be  seen 
from  Table  17. 

TABLE   17. 

Average.  jg™^ 

Aug.       1-15  3393  amps.  .293  volts  per  tank  59  %  12.8  amps,  per  sq.  ft. 

15-31  3196  "  .328  "  "  "  90  %  12.1  "  "  "  " 

Sept.      1-15  3406  "  .39  "  "  "  72^%  12.9  "  "  "  " 

"      15-30  3148  M  .42  "  ll  "  74  %  11.9  "  "  "  " 

Oct.        1-15  2724  "  .44  tl  "  "  89^%  10.6  "  "  "  " 

15-31  2593  "  .435  "  "  "  92  %  9.8  "  "  "  " 

Nov.  1-15  2247  "  .435  "  "  "•  81£%  8.5  "  "  "  " 

15-30  1891  "  .42  "  "  "  93  %     7.2  "  "  "  " 

The  apparent  heavy  loss  for  the  first  period  was  probably 
due  to  absorption  by  the  new  tanks,  leaks,  and  the  unsettled 
condition  of  everything,  but  principally  the  solution  was 
not  well  mixed,  for  the  sample,  indicates  considerably  more 
acid  than  was  actually  purchased  by  the  plant.  The  loss 


42  LEAD   REFINING  BY  ELECTROLYSIS. 

for  the  third  period,  with  a  weaker  electrolyte,  however, 
shows  better  work  than  is  reported  at  present.  Before  Janu- 
ary 17th  some  new  acid  had  been  added.  It  would  appear 
that  the  high  acid  makes  much  higher  acid  loss,  but  that  con- 
clusion is  not  safe,  as  other  conditions  were  changed  very 
much  during  the  first  few  months. 

The  actual  loss  of  acid  experienced  at  the  Trail  refinery 
up  to  the  present,  I  have  been  informed  by  the  management, 
is  about  10  Ibs.  SiF6  per  ton  lead.  Probably  this  has  been 
improved  since  the  figure  was  determined  some  time  ago. 

Tables  18  and  19  give  the  electrical  resistance  of  acid  lead 
fluosilicate  solutions.  Table  18  is  from  determinations  by 
Dr.  E.  F.  Kern  in  my  laboratory.  The  other  table  gives  older 
determinations  made  by  myself,  and  includes  many  solutions 
of  no  practical  importance,  but  at  the  time  the  table  was 
made  it  was  not  known  which  solutions  would  be  most  de- 
sirable. The  temperature  coefficients  are  obtainable  from 
Table  19.  The  conductivity  of  the  solutions  are  also  plotted 
as  Figs.  2,  3,  and  4. 

The  amount  of  gelatine  required  under  good  working  con- 
ditions is  not  great,  and  may  be  taken  at  from  J  Ib.  to  f  Ib. 
per  ton  of  lead  deposited.  Gelatine  in  *lie  form  of  glue  is 
always  used,  as  it  is  cheaper.  I  believe  the  better  grades  of 
glue  the  most  suitable,  for  some  of  the  cheapest  glue  makes 
a  disagreeable  smell  in  the  tank-room.  In  practical  work, 
when  the  glue  in  the  solution  is  about  used  up,  and  it  is 
necessary  to  use  more,  there  will  be  noticed  on  the  cathodes 
a  tendency  toward  the  formation  of  points  on  the  lumps, 
which  are  readily  noticeable  with  a  little  practice.  The  glue 
is  added  in  the  form  of  a  hot,  strong  solution,  and  may  be 
best  put  in  the  circulation-tank  a  little  at  a  time. 


ELECTROLYTES    FOR   LEAD   REFINING. 


43 


The  appearance  of  the  pure  lead  flue-silicate  solution  is 
that  of  a  colorless  liquid.  After  it  has  been  in  use  for  some 
time,  it  has  sometimes  acquired  a  greenish  tinge  from  traces 
of  iron  and  perhaps  nickel  in  the  lead  anodes.  If  the  solu- 
tion is  allowed  to  stand  in  contact  with  air  away  from  the 
reducing  action  of  the  electrodes,  it  acquires  a  brownish  yel- 
low color,  which  at  first  was  thought  to  be  a  ferric  salt,  but 
now  I  believe  it  is  due  to  a  coloring-matter  introduced  with 


12  16 

Grams  Si  F6  per  100  c.  c. 

FIG.  2. 

the  glue.  On  again  using  the  solution  for  refining  it  becomes 
colorless  again,  due  probably  to  the  reduction  of  the  coloring- 
matter  to  the  reduced  or  "leuco"  condition,  which  is  a 
characteristic  of  most  organic  coloring-matters. 

The  metallic  elements  that  enter  into  consideration  as 
possible  constituents  of  the  electrolyte  are  the  elements  usu- 
ally present  in  lead  bullion,  those  that  may  be  in  the  fluo- 
silicic  acid  as  impurities  at  the  start  and  the  iron  binding 


44 


LEAD   REFINING   BY   ELECTROLYSIS. 


30Q  C. 


FIG.  3. 


11     12  18  24  30.5 

Grams  Si  F6  per  100  c.  c.    10  Grams  Pb  per  100  c.  c. 

FIG.  4. 


ELECTROLYTES    FOR   LEAD   REFINING. 
TABLE   18. 


45 


SiF6  Grams 
per  100  cc. 

Lead  Grains 
per  100  cc. 

Temperature. 

Resistance. 

Resistance 
at  20°  C. 
Calculated. 

23.3 

23.6 

19.  5°  C. 

2.34 

2.31 

23.0 

16 

17.   °C. 

1.76 

1.60 

23.0 

12 

19.   °C. 

1.17 

1.12 

23.0 

8 

20.   °C. 

1.09 

1.09 

23.0 

3.4 

20.   °C. 

.87* 

1.06 

16.0 

16.0 

16.   °C. 

2.68 

2.56 

16.0 

12.0 

19.  5°  C. 

2.07 

2.05 

16.0 

8.0 

20.   °C. 

1.49 

1.49 

16.0 

4.0 

20.   °C. 

1.31 

1.31 

12.0 

12.0 

15.  5°  C. 

3.59 

3.24 

12.0 

8.0 

20.  °C. 

2.32 

2.32 

12.0 

4.0 

20.   °C. 

1.63 

1.63 

8.0 

8.0 

15.   °C. 

4.69 

4.19 

8.0 

4.0 

19.   °C. 

2.79 

2.73 

4.0 

4.0 

13.   °C.<I 

9.22 

8 

63.  Of 

85.0 

20.   °C. 

4.84 

4.84 

*  Incorrect.     Correct  figures  is  about  1.06. 

f  Saturated  solution  PbSiF6 ,  specific  gravity,  2.32. 

TABLE   19. 


SiFe  Grams 
per  100  cc. 

Lead  Grams 
per  100  cc. 

oec. 

10°  C. 

20°  C. 

30°  C. 

30.5 

27.8 

2.95 

2.18 

2.10 

1.84 

30.5 

25 

2.66 

2.15 

.84 

1.60 

30.5 

20 

2.07 

1.72 

.57 

1.21 

30.5 

15 

1.74 

1.45 

.23 

1.07 

30.5 

10 

1.48 

1.21 

.04 

.75 

27.1 

25 

3.22 

2.49 

2.13 

1.86 

24 

20 

2.73 

2.24 

.72 

1.52 

24 

15 

2.01 

1.67 

.33 

1.14 

24 

10 

1.62 

1.33 

1.14 

.99 

24 

5 

1.31 

1.45 

1.14 

.87 

21.9 

20 

3.39 

2.68 

2.32 

1.99 

18 

15 

3.50 

2.99 

2.34 

2.09 

18 

10 

2.13 

1.77 

1.50 

1.31 

16.4 

15 

3.80 

3.25 

2.54 

2.28 

12 

10 

4.62 

3.74 

3.35 

2.69 

11 

10 

4.84 

4.13 

3.51 

2.81 

46  LEAD   REFINING   BY   ELECTROLYSIS. 

of  the  tanks.  The  elements  being  considered  then  are  iron, 
zinc,  sulphur,  copper,  nickel,  tin,  antimony,  arsenic,  silver, 
bismuth,  cadmium,  gold,  selenium,  tellurium,  and  other  ele- 
ments in  smaller  quantities.  Of  these  antimony,  arsenic, 
silver,  gold,  copper,  bismuth,  selenium,  tellurium  are  easily 
precipitable  by  lead,  and  consequently  if  they  get  into  the 
solution  they  will  be  thrown  out  by  the  lead  electrodes, 
mostly  by  the  cathodes  I  believe,  for  the  anodes  are  usually 
covered  with  slime,  which  would  prevent  their  reducing,  for 
instance,  much  antimony,  although  the  antimony  of  the 
slime  would  quickly  enough  throw  out  such  an  easily  pre- 
cipitable metal  as  silver. 

Zinc,  iron,  and  nickel,  if  they  find  their  way  into  solu- 
tion remain  there,  as  they  are  not  precipitable  by  the  lead 
electrodes,  nor  can  they  be  in  any  way  thrown  out  on  the 
cathode  by  the  electric  current  so  long  as  there  is  a  fair  amount 
of  lead  in  solution,  which  there  always  is.  Analyses  of  lead 
bullion  show  the  presence  of  iron  and  zinc  in  small  quanti- 
ties, say  .02%.  Whether  the  iron  really  does  dissolve,  I 
doubt,  because  the  slime  usually  contains  from  one-half  to 
two  per  cent  of  iron,  accounting  for  at  least  a  considerable 
part  of  it.  The  slime  also  contains  sulphur  as  sulphides.  As 
iron  is  not  liberated  in  the  lead  smelting-furnace,  but  only 
iron  sulphide,  the  lead  then  probably  takes  up  small  amounts 
of  matte,  and  perhaps  contains  lead  sulphide  too. 

It  is  difficult  to  see  how  any  of  the  sulphur  of  the  lead 
bullion  could  get  into  the  solution,  except  possibly  as  H^S. 
At  any  rate  no  sulphur  has  yet  been  either  observed  in  the 
solution  nor  found  in  the  lead  by  analysis. 

:  The  other  element,  tin,  occupies  practically  the  same  posi- 
tion in  the  scale  of  electromotive  forces  of  solution  that  lead 


ELECTROLYTES   FOR   LEAD   REFINING.  47 

does.  That  is  to  say,  it  takes  about  the  same  electromotive 
force  to  deposit  tin  (from  the  acid  solution)  that  it  does  lead, 
or  to  dissolve  it  from  the  anode.  Consequently  a  mixture 
of  tin  and  lead  can  behave  as  practically  one  metal. 

Dr.  Hans  Mennicke  *  made  some  researches  on  the  refin- 
ing of  tin  lead  alloys,  with  a  solution  of  tin  fluosilicate.  The 
solution  was  more  difficult  to  prepare  than  the  lead  solution. 
No  gelatine  was  added,  but  he  produced  good  tin  deposits 
so  long  as  only  a  little  or  no  lead  was  in  the  solution.  With 
anodes  of  solder  his  deposits  soon  got  spongy.  With  gelatine 
added,  the  deposits  would  probably  have  been  solid.  Both 
tin  and  lead  dissolved  from  the  anodes.  Dr.  Mennicke's  re- 
sults were  not  successful,  but  not  conclusive  either. 

With  about  .02%  tin  in  the  anodes  at  Trail,  some  tin  went 
over  to  the  cathodes.  After  its  presence,  which  was  not  sus- 
pected at  first,  was  proved,  it  was  removed  by  poling  the 
lead  before  casting  when  the  dross  on  the  lead  took  up  the 
tin.  In  such  cases  the  dross  could  be  smelted  to  lead  con- 
taining tin,  and  the  tin  recovered  by  the  usual  softening  pro- 
cess practiced  as  a  preliminary  in  refining  lead  by  the  Parkes 
process.  The  percentage  of  tin  found  in  the  dross  can  be 
calculated  on  the  basis  that  4  or  5%  of  dross  is  produced. 
The  analyses  show: 

Bullion.                                                  Lead  before  Poling. 
Average 0289%  Sn         Average 0063%  Sn 

The  analyses  indicate  that  either  part  of  the  tin  remains 
in  the  slime  or  part  has  already  got  into  the  dross  before 
poling.  The  latter  must  have  certainly  taken  place  and  prob- 
ably the  former  to  some  extent  too.  In  refining  some  bullion 

*  Elektrochemische  Zeitschrift,  Vol.  XII,  112,  134,  161,  180. 


48  LEAD   REFINING   BY   ELECTROLYSIS. 

with  about  4%  tin,  very  considerable  quantities  of  tin  remained 
in  the  slime.  The  tin  in  such  slime  dissolved  out  with  evo- 
lution of  hydrogen  on  treating  with  HC1. 

A  bar  of  fine  solder  (60  tin,  40  lead)  I  once  made  anode 
in  a  lead  fluosilicate  solution  containing  gelatine.  The  anode 
dissolved  regularly  and  the  cathode  deposit  was  excellent. 
The  experiment  was  not  concluded. 

Tin  is  very  rarely  found  in  lead  bullion,  but  in  case  it  is, 
part  or  all  can  be  recovered  from  the  dross  produced  in  melt- 
ing the  cathodes,  and  the  remainder  in  the  slime  can  be  re- 
covered in  several  ways,  if  the  quantity  is  large  enough  to 
make  it  pay. 

The  nature  and  influence  of  the  anode  slime. — Almost 
invariably  in  practical  refining  the  anode  slime  remains 
attached  to  the  anode,  and  very  little  change  in  appearance 
is  noted,  even  when  the  lead  is  nearly  all  gone.  This  is  espe- 
cially the  case  when  the  lead  contains  a  considerable  amount 
of  antimony,  say  10%,  when  there  is  hardly  any  change  in 
the  color  even.  The  slime  is  of  varying  degrees  of  hardness. 
The  proportionate  spaces  occupied  by  the  metal  of  the  slime 
and  the  liquid  with  which  it  is  saturated  can  be  calculated 
with  some  accuracy.  The  data  are:  1  cubic  centimeter  of 
lead  weighs  11.36  grams,  of  antimony  6.7  grams,  of  copper 
8.9  grams,  and  of  silver  10.5  grams.  Allowing  10%  of  lead 
in  the  slime,  the  actual  space  occupied  by  the  slime  from 
11.36  grams  of  alloy  (specific  gravity  practically  the  same  as 
that  of  lead)  is  ordinarily  about  .035  cc.,  leaving  .965  cc.  for 
solution,  or  in  percentages  the  solution  occupies  approxi- 
mately 96-97%  and  the  slime  3-4%.  The  metal  of  the  slime 
is  prevented  from  carrying  any  of  the  current  passing  through, 
at  any  rate  after  it  has  reached  its  final  composition,  by 


ELECTROLYTES    FOR   LEAD   REFINING. 


49 


polarization.  To  illustrate,  suppose  there  is  a  piece  of  some 
metal  lying  below  lead  in  the  electromotive  force  series  for 
fluosilicic  acids,  as  copper,  in  the  electrolyte  between  a  lead 
anode  and  cathode,  Fig.  5. 

Instead  of  passing  through  the  copper,  by  reason  of  its 
greater  conductivity,  the  current  passes  around  the  copper 
on  account  of  its  polarization.  Current  can  only  pass  to  the 


FIG.  5. 

copper  by  depositing  lead  on  it.  On  the  other  side  where 
the  current  leaves,  something  else  would  have  to  dissolve, 
and  this  must  be  copper.  To  deposit  lead  on  one  side  and 
dissolve  copper  from  the  other  would  require  an  electromo- 
tive force  of  about  0.5  volt.  This  is  not  the  actual  truth  of 
the  matter,  because  very  small  currents  can  pass  to  and  from 
electrolytes  and  electrodes  without  any  evidence  of  electrol- 
ysis. With  more  than  an  extremely  small  current  the  cur- 


50 


LEAD   REFINING   BY   ELECTROLYSIS. 


rent  passes  around  the  copper  as  if  it  were  a  piece  of 
glass. 

If  now  the  current  is  increased  so  that  the  fall  of  poten- 
tial in  a  distance  about  equal  to  the  diameter  of  the  copper 
piece  approximates  0.5  volt,  current  will  begin  to  go  through 
the  copper  to  a  considerable  extent,  while  copper  goes  into 
solution  from  one  side. 

The  slime  in  practice  consists  of  a  number  of  different 
metals  of  course,  antimony,  arsenic,  bismuth,  copper,  silver, 
and  gold,  with  some  combined  lead.  For  the  acid  fluosilicate 
solution,  the  electromotive  force  series  has  been  determined 
by  dipping  a  piece  of  lead  and  of  one  of  the  other  metals  into 
the  lead  electrolyte,  by  Dr.  Kern. 

TABLE  20. 


Pb  

0  vo 

its. 

Zn  

+  .  43 

Al.  .  :  . 

+.05 

Sn 

—  03 

Fe  

-.08 

Sb.  . 

..    —.37 

Bi 

-   42 

Cu  

-.43 

As.  . 

.    .    -   52 

Ag 

-   60 

Pt  
C.  .. 

-.63 
.    -.68 

Such  a  method,  however,  cannot  be  accepted  as  giving 
the  correct  figures.  A  better  way  to  determine  these  values 
is  to  prepare  two  fluosilicate  solutions,  one  of  the  lead  and 
one  of  the  other  metal,  separate  the  solutions  with  a  porous 
partition,  dip  the  two  metals  in  their  respective  solutions, 
and  read  the  e.m.f.  with  a  suitable  instrument. 

Somewhat   different   and   more   correct   figures   have   been 


ELECTROLYTES    FOR   LEAD   REFINING. 


51 


obtained  by  placing  lead  fluosilicate  solution  both  inside  and 
outside  of  a  porous  cell,  contained  in  a  beaker.  Such  a  cell 
as  that  shown  in  the  sketch  (Fig.  6)  is  useful  and  handy  for 
Buch  purposes. 

It  consists  of  a  small  piece  of  wood,  which  is  heated  in 
paraffine,  and  after  cooling,  pieces  of  paper,  asbestos  or  cloth 
are  cemented  on  the  wood  with  warm  paraffine.  In  this  par- 
ticular experiment  I  used  ordinary  cardboard  as  diaphragm. 


FIG.  6 

A  piece  of  the  metal  being  tested  is  hung  in  the  inside 
solution  with  a  platinum  wire  and  a  piece  of  lead  dips  in  the 
outside  solution.  A  small  current  is  passed  for  perhaps  five 
minutes  with  the  metal  under  investigation  as  anode.  On 
shutting  off  the  current  the  e.m.f.  is  read  with  a  millivoltmeter. 
It  is  difficult  to  get  a  constant  reading  with  arsenic,  so  I  took 
the  highest  observed.  I  think  the  arsenious  fluosilicate  formed 
at  first  goes  quickly  over  to  arsenious  acid,  which  gives  a 


52  LEAD   REFINING  BY   ELECTROLYSIS. 

lower  e.m.f.  against  lead.  As  the  mechanism  of  the  reaction 
seems  to  be  first  the  formation  of  an  arsenious  salt,  the  high- 
est e.m.f.  is  the  one  with  which  we  are  concerned  when  in- 
vestigating the  possibility  of  arsenic  dissolving  with  the  lead. 
The  series  is  given  in  Table  21. 

TABLE  21. 

Lead 0  volts. 

Arsenic 40 

Antimony 43 

Bismuth 47 

Copper 51 

Silver 97 

These  figures  represent  an  approximately  correct  series 
for  most  other  oxygen-acid  electrolytes.  According  to  it 
each  metal  in  the  series  cannot  be  precipitated  by  those  pre- 
ceding, while  if  the  difference  of  e.m.f.  is  at  all  considerable 
(say  0.1  volt),  each  metal  will  precipitate  those  following. 
When  the  difference  is,  however,  so  small  as  between  anti- 
mony and  bismuth,  no  precipitation  is  usually  observed  to 
take  place  on  dipping  the  higher  metal  into  a  solution  of  the 
next  lower  one.  However,  by  the  electrolysis  of  a  mixed 
solution,  for  example,  copper  and  bismuth  methyl-sulphate, 
copper  can  be  deposited  out  with  little  or  no  bismuth. 

As  we  have  seen  already,  with  ordinary  lead,  such  as  con- 
tains say  3%  of  impurity,  the  space  actually  occupied  by  the 
metal  of  the  adhering  slime  is  only  about  3%  of  the  total. 
Under  the  conditions  of  electromotive  force  existing,  this 
metal  is  practically  non-conducting,  on  account  of  polariza- 
tion. Its  bulk  is,  however,  too  small  to  directly  affect  the 
conductivity  of  the  solution  with  which  it  is  saturated.  It 
does  have  some  small  effect,  however,  by  obstructing  free 
circulation  of  the  electrolyte  in  the  neighborhood  of  the  anode, 


ELECTROLYTES  FOR  LEAD  REFINING.  53 

but  the  total  resistance  thus  introduced  is  extremely  small. 
In  actual  refining,  there  is  rather  a  tendency  for  the  electro- 
motive force  to  fall  off  than  to  increase,  as  the  electrolytic 
action  on  a  set  of  anodes  and  cathodes  goes  on. 

The  usual  thickness  of  an  anode  is  about  one  inch,  and 
the  maximum  thickness  of  slime  then  is  about  one-half  inch. 
Any  current  so  large  or  conductivity  so  low  that  the  drop 
of  potential  in  traversing  one-half  inch  amounts  to  .4  volt, 
or  .8  volt  per  inch,  would  be  as  capable  of  dissolving  arsenic, 
antimony,  bismuth,  and  copper  from  the  surface  layer,  as 
of  dissolving  lead  from  the  solid  electrode  beneath.  With 
an  electrolyte  having  a  resistance  for  the  cubic  inch  unit  of 
1.4  ohms,  the  maximum  current  strength  per  square  foot  per- 
missible would  be  .8  X^X  144  =  about  82  amperes.  As  this 

is  far  beyond  any  current  that  it  is  practicable  to  use,  there 
is  never  any  danger  of  contamination  of  the  solution  or  the 
refined  lead  from  the  direct  attack  of  the  anodes  by  the  cur- 
rent, except  in  the  case  of  tin.  This  statement  applies  only 
to  lead  alloys  with  a  largely  preponderating  proportion  of 
lead. 

Regarding  the  nature  and  constitution  of  the  slime,  using 
as  anode  alloys  of  lead  and  various  other  metals,  it  makes 
some  difference  in  the  amount  of  lead  retained  by  the  slime 
what  the  other  metal  is,  and  how  it  is  combined  with  the 
lead,  and  the  speed  of  working  appears  to  have  some  influ- 
ence, high  current  density  leaving  more  lead  in  the  slime  than 
low-current  density.  There  appears  to  be  no  appreciable 
combination  between  copper  and  lead.  Alloys  of  copper  and 
lead  have  given  a  slime  practically  free  from  lead.  Alloys 
with  40%  copper  and  60%  lead  can  be  treated  easily.  Experi- 


54  LEAD   REFINING   BY   ELECTROLYSIS. 

ments  were  made  by  Dr.  Kern,  which  are  described  in 
Chapter  IX. 

Silver  also  holds  back  very  little  lead.  For  example  silver- 
lead  alloys  of  composition  given  in  Table  22. 

TABLE  22. 

Pb  88%  82.37% 

Ag  9.75%  14.60% 

Cu  1.53%  2.22% 

Sb  .5%  .77% 

Bi  1-11%  -19% 

gave  pure  lead  readily  and  slime  containing  only  1.5%  Pb 
and  2.1%  Pb,  respectively.  Very  likely  what  little  lead  was 
left  was  in  combination  with  the  antimony  and  bismuth. 

That  lead  does  combine  with  some  metals  to  form  com- 
binations not  decomposed  on  electrolyzing  the  alloy  as  anode, 
is  very  forcibly  brought  out  by  Mr.  Senn's  experiment  on  the 
refining  of  lead-platinum  alloy.*  The  alloy  contained  10.10% 
platinum,  and  the  slime  contained  70.45%  Pb  and  .16%  Si02. 
In  another  experiment  the  alloy  contained  10%  platinum 
and  left  a  slime  of  fine  leafy  crystals,  containing  Si02  1.08%, 
Pb  65.30%,  and  Pt  32.93%,  corresponding  to  the  formula 
PtPb2.  Even  when  the  voltage  was  raised  so  high  as  3  volts 
with  oxygen  evolution  at  the  anode,  the  compound  did  not 
decompose  to  any  great  extent.  Lead  peroxide  was  formed, 
but  that  probably  was  deposited  from  the  solution. 

Bismuth  probably  retains  about  one-sixth  of  its  weight 
of  lead,  and  antimony  J  to  i  of  its  weight.  The  amounts 
can,  however,  be  very  different  according  to  the  current  den- 
sities used. 

*  Senn,  Zeitschrift  fur  Elektrochemie,  April  14,  1905. 


ELECTROLYTES  FOR  LEAD  REFINING. 


55 


The  truth  seems  to  be  that  the  compounds  of  lead  and 
other  metals  are  decomposable,  but  only  slowly.  The  slower 
the  treatment  the  less  lead  in  the  slime.  The  maximum 
electromotive  force  available  in  practical  refining  for  the 
decomposition  of  these  compounds  cannot  well  be  over  0.05 
volts  on  the  average  and  0.15  volts  as  a  maximum,  and 
probably  some  of  the  compounds  with  a  small  proportion 
of  lead  are  able  to  resist  this. 

For  the  electrochemical  decomposition  of  antimonides  of 
lead,  etc.,  the  following  experiment  which  I  made  is  interest- 
ing: An  anode  of  hard  lead  with  about  18.8%  antimony 
was  used.  Anode  area  48  square  inches. 

TABLE  23. 


Time. 

Hours  Run. 

Current, 
Amperes. 

Volts. 

Current  Density, 
Amperes  per 
Square  Foot. 

Back  E.M.F. 

8.00 

13 

39 

8.30 

10 

.61 

30 

10.30 

'2.5 

10.5 

.73 

31.5 

11.30 

3.5 

10.5 

.73 

31.5 

1.30 

5.5 

10.5 

.76 

31.5 

3.10 

5.5 

10 

.77 

30 

4.00 

6.3 

9 

.99 

27 

.232 

4.45 

7.0 

8 

.92 

24 

5.00 

7.5 

5.5 

.56 

16.5 

.232 

9.30 

24.0 

1.5 

.53 

4.5 

.304 

The  back  e.m.f.  was  the  voltage  read  with  the  voltmeter 
on  interrupting  the  current,  and  is  a  measure  of  the  chemical 
affinity  of  the  antimony  of  the  slime  for  more  lead  than  it 
is  already  combined  with.  Analysis  of  the  residue  gave  7.83% 
lead. 

The  same  anode  was  further  electrolyzed  with  from  1  to 
2  amperes,  when  the  back  e.m.f.  finally  rose  to  .328  volts, 


56  LEAD  REFINING  BY  ELECTROLYSIS. 

and  the  residue  became  so  fragile  that  it  broke.  The  lead 
antimony  compound  was  then  nearly  entirely  decomposed. 
As  the  difference  of  e.m.f.  of  solution  of  lead  and  antimony 
is  about  .43  volts,  the  e.m.f.  still  falls  short  of  that  necessary 
to  dissolve  antimony. 

The  heat  of  combination  of  lead  with  excess  of  antimony 
is  then  about  17,000  cal. 

Since  the  maximum  voltage  available  in  refining  ordinary 
lead  bullion  for  decomposition  of  antimonides  is  only  about 
.10  to  .15  volts,  the  antimonide  of  lead  cannot  be  nearly 
completely  decomposed  in  usual  practice. 

Pure  lead  was  deposited  by  Dr.  Kern  in  my  laboratory 
from  alloys  of  composition  given  in  Table  24. 

TABLE  24. 

Pb 65.37%  65.56%  82.79%  88.52% 

Bi 7.32%  6.94%  3.42%  2.28% 

Sb 19.51%  18.24%  9.12%  6.08% 

As 5.85%  5.47%  2.73%  1.82% 

Ag 1.95%  1.94%  .97%  .68% 

Cu 1.94%  .97%  .68% 

It  was  necessary  to  work  with  a  low-current  density  of 
about  four  amperes  per  square  foot  with  the  first  two  alloys, 
and  use  thin  anodes,  that  would  last  say,  six  days,  or  what 
amounts  to  the  same  thing,  clean  them  every  six  days.  The 
slime  from  the  first  two  alloys  contained  5.30%  Pb  beside  the 
bismuth,  silver,  copper,  antimony,  and  arsenic.  With  the 
second  two  alloys,  a  continuous  run  was  made  without  clean- 
ing anodes  of  ten  days,  back  e.m.f.  at  end — .07  volts. 

For  an  idea  of  the  amounts  of  lead  held  back  by  antimony, 
copper,  and  bismuth,  the  table  from  Mr.  Serin's  paper  is  in- 
structive. 


ELECTROLYTES  FOR  LEAD  REFINING. 
TABLE  25. 


57 


No. 

Anode  Contains 

Amperes. 

Current 
Amperes, 
Sq.  Dm. 

Amperes, 
Sq.  Ft. 

Dura- 
tion, 
Hours. 

Lead 
De- 
posited, 
Grams. 

Quantity 
Slime, 
W. 

Deposited 
Lead 
Contains 

27 

.92%Cu 

.5 

.59 

5.7 

29 

55.9 

1.64 

NoCu 

28 

.92%  Cu 

.9 

1.07 

10.2 

24 

83.3 

.87 

NoCu 

29 

1.006%  Cu 

1.3 

1.55 

14.9 

18 

90.2 

3.11 

NoCu 

30 

1.006%  Cu 

2 

2.30 

20.2 

9 

69.4 

1.10 

NoCu 

31 

12%  Bi 

.5 

.59 

5.7 

24 

48.3 

NoBi 

32 

12%  Bi 

.9 

1.07 

10.2 

7.25 

25 

i2'72 

NoBi 

33 

12%  Bi 

1.3 

1.55 

14.9 

11 

55.1 

12.60 

No  Bi 

34 

26.67%Bi 

.9 

1.07 

10.2 

17 

59. 

13.25 

No  Bi 

35 

26.67%  Bi 

1.3 

1.55 

14.9 

16.5 

82.6 

36.38 

.94%  Bi 

36 

10.03%  Sb 

.5 

.59 

5.7 

30 

57.9 

8.58 

No  Sb 

37 

10.03%  Sb 

.9 

1.07 

10.2 

8.5 

29.5 

5.19 

NoSb 

38 

10.03%  Sb 

1.3 

1.55 

14.9 

2 

110.3 

18.52 

.13%Sb 

39 

9.81%Sb 

1.3 

1.55 

14.9 

18 

90.3 

10.43 

.05%  Sb 

45 

10.01%  Pt 

.28 

.59 

5.7 

16 

Analysis  of  Slime. 

No. 

Solution. 

Pb% 

Cu% 

Bi% 

Sb  % 

SiC-2  % 

F  % 

27 

28 

23.41 
36.31 

28.47 

9%       Pb—  11%       free 
H2SiF6       falling       to 

29 

19.47 

4.83%    Pb—  8.56% 

30 

io.os 

57.96 

25.12 

free  acid. 

31 

70.49 

32 

42.46 

33 

35  44 

34 

12.4 

83.97 

1.82 

35 

34.83 

60.15 

1.26 

36 
37 

67  71 

.9 

9%  Pb—  11%  free  acid 
falling  to  2.48%  Pb— 

47.52 

1.04 

38 

53.47 

11.5%  free  acid. 

39 

45.00 

45 

The  actual  amount  of  lead  thus  retained  with  anodes  of 
ordinary  grades  of  lead  bullion  is  quite  small.  If  60  pounds 
of  slime  are  produced  per  ton  of  lead,  and  it  contains  12% 
lead,  which  is  a  fair  average,  the  amount  of  lead  in  the  slime 
is  7.2  lbs.  =  0.37%  of  the  total. 
The  electrolysis  of  the  fluosilicate  solution  with  an  insol- 


58  LEAD  REFINING  BY  ELECTROLYSIS. 

uble  anode  is  interesting.     In  this  case  lead  deposits  on  the 
cathode  and  lead  peroxide  on  the  anode  leaving  fluosilicic  acid. 

2PbSiF6  +  2H20  =  Pb02  +  Pb  +  2H2SiF6. 

This  reaction  may  be  useful,  for  instance  if  it  becomes 
necessary  to  reduce  the  percentage  of  lead  in  the  solution 
for  any  reason.  Storage  batteries  have  been  constructed 
to  work  on  this  principle,  but  there  are  mechanical  difficul- 
ties which  have  yet  to  be  overcome.  If  a  purification  of 
refining  solution  became  necessary  the  lead  could  be  removed 
in  this  way  and  the  solution  distilled  or  purified  in  other 
ways. 

From  the  analogy  to  electrolytic  copper  refining  the  ques- 
tion of  purifying  the  electrolyte  was  early  given  a  good  deal 
of  consideration,  and  a  number  of  purifying  schemes  proposed. 
We  now  know  that  the  question  of  purification  of  solutions 
will  never  come  up  in  refining  ordinary  grades  of  bullion.  The 
only  metals  of  the  anodes  that  can  accumulate  in  the  elec- 
trolyte are  iron,  zinc,  nickel,  and  cobalt.  Most  of  the  iron, 
which  is  very  small  in  amount,  remains  in  the  slime  and  the 
others  are  only  present  in  traces.  The  total  amount  of  these 
metals  dissolved  is  probably  not  over  .01%.  The  loss  of  elec- 
trolyte, which  will  be  .3  cubic  foot  or  more  per  ton  lead 
refined,  permits  a  maximum  of  iron,  etc.,  assuming  .01%  to 
dissolve  of  at  most  1.07%  of  these  metals  in  the  solution, 
which  is  too  small  to  be  serious. 

As  the  preparation  of  pure  lead  may  be  of  interest,  the 
following  quotation  from  a  paper  by  Dr.  Kern  and  myself 
on  the  "Lead  Voltameter,"*  is  given: 

*  Trans.  Am.  Electrochemical  Society,  Vol.  VI,  page  67. 


ELECTROLYTES  FOR  LEAD  REFINING.  59 

"  The  solution  was  diluted  so  as  to  contain  17  grams  of 
PbSiF6  and  7  grams  of  free  H2SiF6  in  100  cc.  solution.  After 
adding  one  gram  of  gelatine  (dissolved  in  hot  water)  to  2000 
cubic  centimeters  of  solution,  the  electrolyte  was  rendered  abso- 
lutely pure,  in  respect  to  metals  which  can  deposit  with  lead, 
by  electrolyzing  for  several  days,  using  electrodes  of  refined 
lead.  The  anodes  were  wrapped  with  two  thicknesses  of 
clean  linen,  so  as  to  prevent  the  impurities  from  dropping  off 
and  floating  in  the  electrolyte.  The  small  amount  of  solu- 
ble impurities  in  the  electrolyte  was  due  principally  to  the 
impurities  in  the  white  lead  used  for  making  the  solution. 
The  electrolysis  was  continued  for  four  days  at  temperatures 
between  17°  C.  and  57°  C.,  using  a  current  density  at  the 
electrodes  of  10  to  12  amperes  per  square  foot.  A  small 
amount  of  ' anode  sludge'  remained  behind,  and  in  order 
to  prevent  it  from  being  oxidized  by  the  atmosphere  and 
subsequently  going  into  solution,  melted  vaseline  was  poured 
on  the  surface  of  the  electrolyte.  The  deposit  which  formed 
on  the  cathode  was  smooth,  dense,  and  non-crystalline. 

"  After  purifying  the  electrolyte,  about  800  grams  of  abso- 
lutely pure  lead  was  made  by  electrolysis,  using  ordinary 
refined  lead,  wrapped  with  clean  linen,  for  the  anodes.  The 
refined  lead  which  was  deposited  on  the  cathode  was  fur- 
ther refined  by  reversing  the  current  density  and  re-deposit- 
ing it  on  new  cathodes.  The  solution  was  protected  from 
the  atmosphere  by  a  covering  of  melted  vaseline.  The  puri- 
fied lead  was  melted,  cast  into  a  thin  plate,  and  then  rolled 
into  sheets  about  ^  inch  to  TV  inch  thick.  The  sheets  were 
cut  into  strips  of  suitable  size  and  used  as  anodes  for  the 
lead  voltameter.  No  residue  was  left  on  dissolving  the  puri- 
fied anodes  by  electrolysis." 


CHAPTER   II. 

CHEMISTRY  OF  SLIME  TREATMENT. 

LEAD  slime  contains  originally  metallic  lead,  copper,  gold, 
silver,  bismuth,  antimony,  arsenic,  sulphur,  and  occasionally 
probably  other  elements,  tin,  selenium,  and  tellurium.  For 
analyses  see  Table  26.  The  object  of  its  refining  is  to  recover 
especially  the  gold  and  silver,  but  the  bismuth,  antimony, 
copper,  and  lead  are  also  valuable  and  should  be  saved. 

There  are  several  different  methods  of  treatment,  based 
on  different  chemical  or  physical  properties  of  the  various 
metals. 

These  methods  are  distillation,  amalgamation,  fusion  to 
alloy,  followed  by  chemical  or  electrochemical  treatment  of 
the  alloy,  fusion  to  bullion  and  slag,  fusion  to  matte  and  slag, 
electrolytic  refining  of  the  slime  direct,  dry  treatment  with 
chlorine  and  separation  of  the  chlorides  by  distillation,  and 
various  wet  chemical  and  electrochemical  methods  of  treat- 
ment. 

Distillation. — The  temperatures  necessary  to  distil  the 
metals  could  easily  be  obtained  in  an  electric  furnace,  and 
nothing  would  be  simpler  than  to  separate  the  metals  in  this 
way,  apparently.  The  energy  requirement  would  not  be 
large.  The  trouble  is  that  the  boiling-points  of  the  three 
principal  metals,  lead,  antimony,  and  silver,  lie  too  close 
together.  That  antimony  boiled  as  high  as  1600°,  as  deter- 

60 


CHEMISTRY  OF  SLIME  TREATMENT 


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62  LEAD   REFINING  BY  ELECTROLYSIS. 

mined  by  V.  Meyer,  did  seem  surprising,  as  antimony  is  re- 
garded in  smelting  as  a  volatile  element.  Its  volatility  in 
smelting  is  due  to  the  low  boiling-point  of  its  oxide,  how- 
ever. I  was  unable  to  volatilize  any  antimony  on  heating 
it  in  a  carbon  crucible  in  an  anthracite  fire,  and  the  tem- 
perature was  certainly  high  enough  to  melt  steel. 

Messrs.  Moissan  and  Watanabe  *  report  the  results  of  experi- 
ments on  the  distillation  of  alloys  of  nearly  equal  parts  cop- 
per and  silver;  and  of  tin  64%  and  silver  35%,  and  of  lead 
53%  and  silver  46%.  The  alloys  were  heated  for  various 
periods  in  an  electric  furnace  and  the  residual  metals  weighed 
and  analyzed.  I  have  plotted  the  results  as  Figs.  7,  8,  and  9. 
The  last  two  figures  are  based  on  only  three  determinations 
each,  and  the  curves  are  in  consequence  not  necessarily  en- 
tirely correct  in  form.  They  show  no  complete  separation 
of  metals  by  distillation. 

Amalgamation. — Lead,  copper,  gold,  silver,  and  bismuth 
amalgamate  easily,  and  arsenic  and  antimony  do  not,  so  that 
a  separation  might  be  made.  Fresh  unoxidized  slime  has 
been  ground  with  mercury  and  some  fluosilicate  electrolyte 
in  a  mortar,  and  the  mercury  takes  up  a  portion  of  the  sil- 
ver, gold,  copper,  and  lead,  but  the  separation  is  very  far 
from  complete,  probably  because  the  metallic  arsenides,  anti- 
monides,  and  other  compounds  present  in  the  slime  are  too 
stable  to  be  decomposable  by  mercury.  Even  after  the  sep- 
aration was  made  by  amalgamation,  considerable  still  remains 
to  be  done  before  the  metals  are  finally  recovered.  The  bul- 
lion could  be  retorted  as  it  is  usually  done  in  amalgamation 
silver  mills,  or  an  electrolytic  method  for  extracting  silver, 

*  Comptes  Rendus  1,  CXLIV,  1907.     Number  11,  page  16. 


CHEMISTRY  OF  SLIME  TREATMENT. 


63 


copper,    lead,    and    bismuth    from   the   amalgam      might     be 
devised. 


SO;* 
60{i 
40^ 
20* 


29,8$ 


FIG.  9. 


85.3* 


Fusion    to    alloys. — Slime     oxidizes    rather    readily    when 
dry,  and  some  varieties  will  inflame  spontaneously  on  drying, 


64  LEAD  REFINING  BY  ELECTROLYSIS. 

so  that  to  melt  it  without  oxidation  one  has  to  be  careful. 
A  good  way  to  do,  experimentally,  is  to  put  the  still  moist 
slime  in  a  crucible,  and  cover  the  crucible  while  melting. 
Even  then,  the  escaping  steam  is  liable  to  oxidize  some  of 
the  slime,  especially  the  antimony.  Whether  steam  actually 
does  oxidize  finely  divided  antimony  with  production  of 
hydrogen,  has  not  been  definitely  determined.  Some  slime, 
especially  slime  which  is  rather  dense,  from  anodes  rather 
lower  in  lead,  containing  say  10%  antimony,  melts  with  the 
formation  of  little  or  no  slag  to  a  clean  alloy. 

As  lead  is  rather  objectionable  in  alloys  that  are  to  be 
treated  with  solutions  containing  sulphuric  or  hydrofluoric 
acids,  on  account  of  the  insoluble  lead  sulphate  or  fluoride 
that  forms,  it  is  desirable  to  get  the  lead  out  as  a  slag  in 
melting,  if  possible.  This  may  be  done  quite  readily  with 
slime  from  ordinary  bullion  by  mixing  the  fresh  slime,  pressed 
as  dry  as  possible  on  the  filter,  with  enough  concentrated  HC1 
to  convert  the  lead  present  into  lead  chloride.  If  the  slime 
contains  say  12%  of  lead,  about  12%  by  weight  of  40%  HC1 
is  right.  Some  reducing  agent,  as  flour,  may  also  be  added 
advantageously.  On  melting  the  moist  mixture  in  a  cruci- 
ble an  alloy  is  produced  containing  silver,  gold,  bismuth, 
some  of  the  copper  and  a  large  part  of  the  antimony  of  the 
slime,  with  a  slag  of  lead  chloride  and  antimony  oxide,  and  a 
scum  of  copper  and  lead  sulphides.  The  slag  and  scum  may 
go  back  to  the  lead  blast-furnace  of  course,  where  its  values 
will  be  covered,  while  the  metal  may  be  electrically  or  chem- 
ically refined.  This  melting  method  on  one  occasion  failed, 
and  the  hydrochloric  acid  escaped,  no  lead  chloride  or  other 
slag  being  formed.  The  slime  was  a  heavy  one  from  lead 
containing  much  antimony. 


CHEMISTRY  OF  SLIME  TREATMENT.  65 

As  an  example,  a  light  slime  containing  bismuth  was  washed 
and  a  moisture  determination  made  to  get  the  dry  weight, 
which  was  found  to  be  300  gr.  One  hundred  grams  lead  chlo- 
ride and  about  30  cc.  concentrated  HC1,  and  a  few  grams  tar- 
taric  acid  as  reducing  agent  were  added  and  the  whole  stirred 
together.  The  mixture  was  added  in  portions  to  a  small  cru- 
cible and  heated  to  a  red  heat.  A  good  deal  of  smoke  from 
burning  tartaric  acid  and  arsenic  came  off.  The  products 
were  135  grams  of  metal  and  about  140  of  slag,  and  some 
additional  slag  was  absorbed  by  the  crucible.  About  20 
grams  of  scum,  that  looked  like  galena,  remained  in  the 
crucible. 

On  analysis  the  slag  was  found  to  contain  9%  antimony, 
1%  iron,  trace  of  bismuth  and  arsenic,  and  1%  copper,  the 
remainder  being  mostly  lead  chloride.  The  metal  contained 
30.2%  silver,  a  trace  of  lead,  2.5%  copper,  and  13.0%  bis- 
muth. The  remainder  was  mostly  antimony,  not  determined 
however. 

In  another  experiment,  224  grams  slime  (dry  weight)  melted 
with  HC1,  but  without  lead  chloride,  gave  82  grams  metal  and 
75  grams  of  slag. 

A  complete  separation  of  lead  is  thus  obtained,  while  all 
the  bismuth  goes  into  the  metal  as  well  as  about  80%  of  the 
antimony. 

Fused  lead  chloride  makes  an  excellent  electrolyte  for 
depositing  metals,  so  the  slag  was  electrolyzed  with  carbon 
electrodes  at  a  red  heat. 

There  are  present  Sb203  and  PbCl2.  As  the  reaction, 
Sb203+3PbCl2  =  2SbCl3+3PbO  can  only  take  place  with  loss 
of  energy,  it  need  not  be  considered  to  occur.  The  heats  of 
formation  of  these  compound  are: 


66  LEAD  REFINING  BY  ELECTROLYSIS. 

Sb203  =166,900  cal. 
3PbCl2  =  251,700   " 


418,600   " 

2SbCl3  =  182,800  cal. 
3PbO   =152,400   " 


335,200    " 

Therefore  reduction  by  carbon  ought  to  yield  metallic  anti- 
mony in  preference  to  lead  as  the  reaction,  Sb203  +  3C  =  2Sb  +  30 
requires  79,420  cals.,  and  the  reaction  Sb203  +  3C  +  3PbCl2  = 
3Pb  +  2SbCl3  +  3CO  requires  more,  namely,  146,320  cals. 

Reduction  by  carbon  could  only  take  place  at  a  rather 
elevated  temperature,  as  the  reactions  are  stongly  endothermic 
at  low  temperatures,  and  the  volatility  of  both  lead  chloride 
and  antimony  trioxide  is  too  great  at  high  temperatures. 
Electrolytic  reduction  of  the  slag  with  carbon  anode,  which 
carries  out  the  same  reactions,  and  carbon  cathode  was  tried 
with  some  success,  and  18  grams  of  metal  reduced  with  high 
current  efficiency,  containing:  silver  14.5%,  copper  4.7%,  lead 
39.0%,  antimony  40.0%. 

The  presence  of  all  this  silver  indicates  that  there  were 
either  metal  shot  in  the  slag  to  start  with,  or  some  silver  was 
reduced  from  the  scum.  The  quantity  of  silver  in  this  pro- 
duct was  relatively  small,  about  5.85%  of  the  total  accounted 
for.  Probably  the  heat  in  the  original  melting  was  not  high 
enough  to  thoroughly  melt  the  slag.  The  temperature  was 
only  a  red  heat. 

The  treatment  of  the  alloy  and  similar  artificial  alloys 
was  attempted  by  various  methods,  dry  and  wet. 


CHEMISTRY  OF  SLIME  TREATMENT.  67 

For  treatment  with  chlorine  we  consider  the  heat  of 
combination  of  the  various  metals  present,  with  chlorine,  the 
figures  being  as  follows: 

TABLE  27. 

$  PbCl2 41,950   cal. 

CuCl 35,400  " 

%  SbCl3 30,467  " 

i  BiCl3 30,233  ", 

AgCl 29,000     " 

Bismuth  is  capable  of  forming  a  bismuth  bichloride,  of 
which  the  heat  of  formation  is  probably  somewhat  greater. 
Chlorine  would  then  apparently  take  out  the  copper,  and 
then  the  bismuth.  On  passing  chlorine  into  the  metal  in  a 
crucible  much  volatile  SbCl3  came  off  at  once,  which  was  not 
desired  or  expected. 

The  heat  of  formation  of  cupric  chloride  from  cuprous 
chloride  (CuCl  +  Cl  =  CuCl2)  is  16,000  cals.,  and  it  would 
accordingly  act  on  the  alloy  as  a  chloridizing  agent.  Experi- 
mentally it  could  be  applied  more  conveniently  and  in  better 
regulated  amount  than  chlorine.  I  accordingly  melted  to- 
gether an  alloy  of  this  composition: 

Antimony 65.2% 

Copper 13.2% 

Bismuth 21.6% 

This  was  put  in  a  porcelain  crucible  with  some  PbCl2  and 
NaCl  for  a  cover,  and  55.5%  of  anhydrous  CuCl2  by  weight 
added,  or  enough  to  chloridize  the  copper  of  the  alloy  to  CuCl 
and  the  bismuth  to  BiCl2. 

No  such  reactions  took  place.  Antimony  chloride  came 
off  in  large  quantity.  The  resulting  alloy  contained  31.5% 


68  LEAD  REFINING  BY  ELECTROLYSIS. 

copper  and  the  slag  38%.  The  metal  also  contained  19-20% 
bismuth. 

In  general  it  has  been  found  that  precipitation  of  one 
metal  by  another  from  a  fused  melt  is  greatly  influenced  by 
the  formation  of  compounds  among  the  metals  of  the  alloy 
themselves,  and  that  the  reactions  are  rarely  complete  and 
do  not  always  proceed  as  indicated  by  the  formation — heat 
figures. 

Dry  chlorination  of  slime. — The  metals  can,  however,  be 
separated  by  converting  them  into  chlorides  and  fraction- 
ally distilling  the  chlorides. 

TABLE  28. 

Arsenic       chloride  AsCl3  boils  at    134°  C. 

Antimony        "  SbCl3     "      "     223°  C. 

Bismuth          "  BiCl3      "      "     435°  C. 

Copper  "  CuCl      "      "   1000°  C. 

Lead  "  PbCl2     "      "  white  heat. 

For  conversion  into  chlorides  there  is,  of  course,  no 
necessity  of  first  melting  to  an  alloy,  as  the  chlorine  may  be 
passed  into  the  slime. 

In  one  experiment  250  grams  of  slime,  containing  about 

Copper 12.5% 

Bismuth 20.   % 

Arsenic 15 . 7% 

Antimony 11 .3% 

Silver 18.3% 

Lead 10    % 

was  treated  in  a  flask  with  chlorine.  133  grams  of  chloride 
distilled  over,  but  the  chlorine  did  not  penetrate  the  mix- 
ture thoroughly.  There  is  no  difficulty  about  removing 


CHEMISTRY  OF  SLIME  TREATMENT.  69 

arsenic  and  antimony  as  chlorides,  in  this  way,  leaving  lead, 
copper,  and  bismuth  chlorides  in  the  residue,  and  also  in 
distilling  off  the  bismuth  if  desired. 

The  heat  generated  by  the  reaction  of  cold  chlorine 
on  cold  arsenic,  for  example,  is  sufficient  to  vaporize  it  and 
raise  it  to  a  very  high  temperature,  but  the  thermochemical 
data  to  determine  this  temperature  are  not  at  hand.  The 
reaction  on  the  other  metals  is  just  as  violent,  so  that  on 
operations  of  any  magnitude  no  external  heating  is  necessary 
to  drive  off  the  arsenic,  antimony  and  bismuth,  and  probably 
the  temperature  would  go  beyond  the  boiling-points  of  lead 
and  copper  chlorides,  leaving  silver  and  gold  bullion  in  the 
melted  state,  with  some  slag  of  copper  chloride,  if  the  right 
amount  of  chlorine  was  used.  This  is  not  an  entire  innovation, 
for  the  treatment  of  gold  with  chlorine  for  removing  silver  and 
base  metals  has  been  successfully  carried  out  for  years,  the 
process  having  been  originated  by  Mr.  F.  B.  Miller  of  the  Syd- 
ney Mint,  in  1867.*  Clay  crucibles  are  stated  to  be  used, 
rendered  impenetrable  to  the  silver  chloride  by  dipping  them 
in  hot  concentrated  borax  solution  before  using. 

The  chlorine  for  treating  slime  could  be  readily  made  by 
electrolyzing  fused  lead  chloride,  which  is  one  of  the  easiest, 
if  not  the  easiest,  of  all  fused  salts,  to  decompose  electrolyti- 
cally.  It  has  never  been  done  commercially  because  lead 
chloride  is  not  a  raw  material,  but  in  the  chlorination  of  slime 
the  chlorides  of  copper,  silver,  antimony,  and  bismuth  pro- 
duced are  reducible  by  lead,  giving  the  metals  and  lead 
chloride. 


*  Rose's  Metallurgy  of  Gold,   page  441.     Eissler's  Metallurgy  of  Gold, 
page  615. 


70  LEAD   REFINING  BY   ELECTROLYSIS. 

A  difficulty  is  the  storage  of  chlorine.  The  electrolytic 
plant  should  run  continuously  and  the  chlorine  would  be 
required  intermittently.  This  has  probably  been  one  of  the 
reasons  why  chlorination  has  not  been  applied  more  in  metal- 
lurgy. It  seems  to  me  that  an  easy  way  to  store  chlorine 
is  to  condense  it  by  means  of  sulphur  to  sulphur  chloride, 
and  produce  chlorine  therefrom  by  warming  the  sulphur  chlo- 
ride. At  temperatures  below  30°  C.  the  mixture  saturated 
with  chlorine  has  the  composition  SC14.  At  6°  the  compo- 
sition is  SC12,  and  at  139°  SCI.  Chlorine  is  very  readily 
absorbed  by  the  sulphur  and  its  chlorides  at  the  appropriate 
temperatures.  In  a  paper  on  his  chlorine  smelting  process 
Ashcroft  *  has  described  methods  of  pumping  and  drying 
chlorine.  A  special  process  for  drying  chlorine  is  not  neces- 
sary in  presence  of  sulphur,  as  sulphur  chlorides  decompose 
water.  The  chlorine  vaporized  from  sulphur  chloride  will 
contain  some  sulphur,  but  this  is  a  desirable  circumstance, 
as  any  metallic  oxides  are  readily  converted  to  chlorides  by 
sulphur  chloride,  even  such  oxides  as  those  of  aluminum  and 
silicon  being  convertible  in  this  way.f 

The  conversion  of  the  chlorides  of  antimony  and  bismuth 
into  metal  is  easy  in  the  case  of  bismuth,  because  all  that 
it  is  necessary  to  do  is  to  decompose  the  bismuth  chloride 
with  melted  lead.  Antimony  chloride  boils  below  the  melt- 
ing-point of  lead  and  well  below  the  melting-point  of  anti- 
mony, so  that  it  would  have  to  be  passed  into  melted  lead 
as  a  vapor. 

It  has  been  proposed  f  to  treat  slime  with  chlorine  in  the 


*  Electrochem.  and  Metall.   Industry,  Vol.  IV,   1906,  page  96. 
fU.  C5.  patent,   Betts,   712640,   November  4,    1902. 


CHEMISTRY  OF  SLIME  TREATMENT.  71 

presence  of  water,  producing  a  solution  containing  antimony, 
arsenic,  and  bismuth  trichlorides,  and  a  precipitate  of  lead 
chloride  and  cuprous  chloride,  insufficient  chlorine  being 
used  to  chlorinate  the  silver  and  gold  (which  is  possible  on 
account  of  the  lower  combining  heat  of  silver,  and  especially 
of  gold  for  chlorine),  filtering,  boiling  off  arsenic  and  antimony 
chlorides  and  water,  and  taking  up  the  residue  with  water 
to  remove  lead  chloride.  The  distillation  of  antimony  chlo- 
ride solution  is  not  as  satisfactory  as  might  be  believed  from 
reading  descriptions  of  it,  because  it  decomposes  into  oxide 
and  hydrochloric  acid,  unless  a  large  excess  of  HC1  is  used. 
It  would  be  difficult  to  find  materials  for  carrying  out  the 
distillation  on  a  large  scale.  The  dry  chlorination  is  then 
much  superior,  in  which  case  the  heat  of  reaction  will  be  suffi- 
cient for  the  distillation,  so  that  the  apparatus  question  is 
not  a  difficult  one  at  all  in  that  case. 

Direct  fusion  with  soda. — Most  slime,  and  slime  from 
ordinary  grades  of  bullion,  if  dried  and  warmed,  is  very  apt 
to  oxidize  so  rapidly  as  to  sinter  or  turn  yellow,  according 
to  its  composition.  The  oxidation  takes  place  in  two  stages; 
one  is  a  slow  oxidation  at  a  low  temperature,  the  product 
being  black  and  soft.  If  the  temperature  is  high  enough, 
the  slime  oxidizes  rapidly,  and  if  it  contains  considerable  anti- 
mony, say  40  or  50%,  it  is  not  so  apt  to  sinter,  but  yields  a 
yellow  product.  This  is  mainly  antimony  pentoxide,  and 
it  is  a  difficult  material  to  treat.  It  is  insoluble  in  acids  and 
infusible.  It  fluxes  with  soda,  but  only  at  a  high  tempera- 
ture. Heated  with  powdered  charcoal,  however,  it  may  be 
reduced  to  the  very  easily  fusible  trioxide.  The  same  end 
may  be  accomplished  by  heating  it  with  raw,  unoxidized 
slime. 


72  LEAD  REFINING  BY  ELECTROLYSIS. 

At  Trail  the  slime  contains  about  30%  antimony,  20% 
silver,  10%  copper,  6%  arsenic,  10%  lead,  beside  gold. 

The  process  worked  out  by  the  Canadian  Smelting  Works 
and  in  use  there  still  has  been  described  as  follows:  It  was 
originally  intended  to  boil  the  slime  with  sodium  hydrate 
and  carbonate  to  dissolve  out  the  antimony,*  oxidation  being 
performed  by  drawing  a  current  of  air  through  the  solution 
and  melting  the  remainder  in  a  magnesia-lined  reverberatory 
to  a  dore  bullion.  The  antimony  failed  to  dissolve  in  more 
than  very  small  quantities,  so  this  step  was  omitted  from 
the  process,  and  the  slime  melted  directly.  Copper  is  diffi- 
cult to  remove  in  this  way,  and  this  was  got  around  to 
some  extent  by  skimming  all  the  dross  possible  from  the 
lead  before  making  anodes. 

The  slime  is  placed  in  iron  wheelbarrows  or  trucks  and 
wheeled  into  a  large  brick  oven,  with  thin  walls,  which  can 
be  heated  evenly  with  coal  fired  outside.  After  the  slime 
is  pretty  well  dried,  it  is  dumped  into  a  brick  stall,  where 
there  is  a  good  draught,  when  it  ignites  and  roasts,  copious 
fumes  of  arsenic  coming  off.  After  oxidizing  it  is  melted 
down  in  a  reverberatory  with  soda  to  a  dore  bullion.  The 
slag  averages  about  30-40%  Sb,  5-8%  Cu,  10-15%  Pb,  with 
considerable  silica,  and  from  200  to  600  ozs.  of  silver  per  ton. 
The  Trail  refinery  is  using  this  process  temporarily,  until 
they  have  completed  their  experiments  to  devise  a  better 
process.  To  get  the  right  amount  of  oxidation,  which  varies 
with  unavoidable  variations  in  composition  and  roasting  of 
the  slime,  either  coal  dust  or  nitre,  as  the  case  may  be,  is 
added  to  the  melt  in  the  furnace.  The  melting  part  of  the 

*  Mines  and  Minerals,  Vol.  25  (1905),  page  28. 


CHEMISTRY  OF  SLIME  TREATMENT.  73 

process  is  not  satisfactory  on  account  of  the  high  tempera- 
ture and  metal  losses,  nor  are  by-products  (except  copper) 
recovered  in  marketable  form. 

In  this  process  the  antimony  is  probably  slagged  off  partly 
as  Sb205  combined  with  some  soda,  and  as  Sb203. 

Melting  without  fluxes,  slagging  antimony  as  Sb203. — 
Antimony  trioxide  melts  below  a  red  heat,  but  contact  with 
air  or  oxidizing  gases  makes  the  melted  trioxide  soon  get 
pasty  and  finally  infusible.  This  is  because  the  reaction 
Sb203  +  20  =  Sb205  is  quite  vigorous.  If  powdered  coal  or 
ground  antimony  be  stirred  in  the  product,  another  reaction 
takes  place,  and  the  easily  fusible  trioxide  results  again. 

Sb203  +  20  =  Sb205+ 64,300  cal.  at  0°, 
Sb205+2C  =  Sb203  +  2CO-5980  cal.  at  0°. 

At  700°  the  latter  reaction  is  still  slightly  endothermic, 
but  it  occurs  readily  enough.  Perhaps  some  of  the  reduc- 
tion, in  the  case  of  carbon,  is  done  by  the  CO  produced,  with 
evolution  of  heat.  Unoxidized  slime  will  perform  the  reduc- 
tion as  well. 

By  melting  slime  which  is  only  partially  oxidized,  or 
proper  mixtures  of  thoroughly  oxidized  and  unoxidized  slime, 
and  keeping  any  excess  of  oxidizing  gases  carefully  away 
during  the  melting,  a  black,  glassy,  and  extremely  fusible 
slag  results,  and  a  metallic  product  containing  the  silver  and 
variable  amounts  of  lead,  antimony,  and  copper,  according 
to  the  proportion  of  oxygen  present.  As  slime  contains  usu- 
ally sulphur,  a  matte  containing  20-30%  silver  and  about 
50%  copper  is  also  produced,  if  there  is  not  too  much  oxygen 


74 


LEAD  REFINING  BY  ELECTROLYSIS. 


present.  The  difficulties  are  in  getting  just  the  right  pro- 
portion of  oxygen  and  loss  of  antimony  trioxide  by  volatili- 
zation. At  the  temperature  necessary  to  melt  the  silver 
antimony  trioxide  volatilizes  very  fast.  If  some  antimony 
and  lead  are  left  in  the  silver  by  deficiency  of  oxygen,  the 
temperature  may  be  much  reduced,  but  the  metal  requires 
another  treatment  to  remove  antimony  and  lead.  If  the 
melt  is  not  well  covered,  the  pentoxide  will  form,  so  that  a 
reverberatory  furnace  is  not  suitable,  both  for  this  reason 
and  on  account  of  the  volatilization  difficulty.  No  satisfac- 
tory crucible  has  been  found,  as  the  slag  attacks  most  cru- 
cibles rapidly.  My  experiments  indicate,  however,  that  a 
cast-iron  crucible  will  do  quite  well.  The  electric  furnace  is 
the  remaining  means,  and  is  entirely  feasible  from  a  power 
standpoint  and  admits  of  melting  large  quantities  rapidly 
with  little  loss.  The  specific  heat  of  slime  can  be  roughly 
•calculated  as  follows: 


Heat  in  melted  silver 
Heat  in  Sb2O3 
Heat  in  Pb  O 
Heat  in  Cu^S 
Volatilization  AS2O3 


TABLE  29. 


at  960°  per  Ib.    89.15  Ib.  cals. 


960° 
960° 
960° 
960° 


Heating  and  vaporizing  H2O  '     960° 


200 
150 
200 
200 
700 


These  are  the  principal  constituents.  The  figures  are 
not  known  for  antimony,  lead,  and  arsenic  oxides,  and  can 
only  be  very  roughly  got  from  comparison  with  compounds 
for  which  the  exact  figures  are  known.  The  above  figures 
will  do  for  our  present  purpose,  as  will  be  readily  seen  below. 

Suppose  the  slime  contains 


CHEMISTRY  OF  SLIME  TREATMENT.  75 

TABLE  30. 

H2O  15%  =  102. 5  Ib.  cals. 
Silver  30%=  27.0 
Sb2O3  30%=  60.0 
As2O3  10%=  20.0 

PbO  10%=   15.0 

Cu2S  5%   =   10 

Heat  required  in  Ib.  cals.     234 . 5 

(The  pound  calorie  is  the  amount  of  heat  required  to 
heat  one  pound  of  water,  one  degree  centigrade,  and  is  equiv- 
alent to  .00052  K.W.  hours,  or  .00069  E.H.P.  hours,  in  elec- 
tric energy.) 

The  heat  necessary  at  100%  efficiency  per  pound  of  slime 
is  0.12  K.W.  hours;  at  50%  efficiency,  which  is  easily  obtained, 
and  for  lead  producing  80  Ibs.  of  slime  per  ton,  20  K.W.  hours 
would  be  necessary  for  melting.  This  is  so  small  that 
quite  large  proportionate  errors  in  the  specific  heats  above 
would  not  make  any  practical  difference. 

Not  all  types  of  electric  furnace  would  be  suitable.  Con- 
tact with  hot  carbon  would  tend  to  reduce  the  slag  and  render 
the  precipitated  metal  too  base.  A  furnace  heated  by  radi- 
ation from  an  arc  or  a  heated  carbon  rod  would  do,  but  a 
furnace  of  the  resistance  type,  in  which  the  heat  is  gener- 
ated in  a  narrow  conductor  of  the  metal,  would  seem  to  be 
best  adapted.  The  heating  current  may  either  be  induced 
as  in  the  Colby  or  Kjellin  *  and  similar  furnaces.  That 
electric  furnaces  will  be  used  in  slime  and  silver  melting  is 
probable.  Small  induction  furnaces  for  melting  steel  and 


*  Colby,  U.  S.  patents  428378  and  428379,  May  20,  1890;  Gin., 
771872,  Oct.  11,  1904;  Schneider,  761920,  June  7,  1904;  Betts,  U.  S. 
Patent  816558,  April  3,  1905. 


76  LEAD  REFINING  BY  ELECTROLYSIS. 

brass  are  now  on  the  market  and  in  successful  use,*  but  the 
material  of  which  the  crucibles  are  made  would  have  to  be 
changed  for  slime  melting,  and  some  arrangement  would  be 
necessary  to  catch  the  fumes  given  off. 

When  the  slime  contains  bismuth  in  appreciable  quantity 
the  melting  process  is  at  its  best,  because  the  bismuth  is  in- 
termediate in  oxidizability  between  silver  on  the  one  hand, 
and  lead  and  antimony  on  the  other,  and  as  a  consequence 
the  percentage  of  oxidation  does  not  need  to  be  so  carefully 
controlled  to  insure  a  separation  of  gold  and  silver  from  lead 
and  antimony.  In  case  the  oxygen  is  higher  than  usual, 
more  bismuth  is  slagged;  in  case  the  oxygen  is  lower,  more 
bismuth  goes  into  the  dore*,  while  in  either  case  the  antimony 
and  lead  remain  almost  entirely  in  the  slag,  and  the  silver  as 
metal.  Also  the  presence  of  bismuth  in  the  silver  increases 
its  fusibility,  so  that  the  melting  temperature  need  not  be 
nearly  so  high.  The  slag  high  in  Sb20s  is  so  fusible  that  it 
melts  below  a  red  heat. 

These  facts  are  brought  out  well  from  the  analysis  of  the 
products  resulting  from  the  melting  down  of  some  partially 
air-oxidized  slime  in  my  laboratory. 

TABLE  31. 

Metal  35  Gr.  Slag  80  Gr.          Matte  about  2  Gr. 

Au 78% 

Ag 66.23% 

Bi 20.3%  2.95%  30% 

Cu 5.1%  1.15%  46.3% 

Sb 1.3%  28%  None. 

Pb 8%  34.9%  None. 

The  value,  5%  for  copper  in  metal,  is  probably  too  high, 
as  the  sample  may  have  contained  a  little  intermixed  matte. 

*  Electrochemical  and  Metallurgical  Industry,  232,  1907. 


CHEMISTRY  OF  SLIME  TREATMENT.  77 

On  cooling  the  bar  bismuth  liquates  out  in  little  drops 
that  can  be  knocked  off.  These  contained  little  beside  bis- 
muth. The  analysis  showed  87%  bismuth,  6%  silver. 

The  treatment  of  these  products  can  be  carried  out  suc- 
cessfully. The  bullion  may  be  parted  by  the  methyl-sulphate 
method,  as  described  in  Chapter  IV,  and  the  slag  may  be  freed 
from  bismuth,  if  required,  by  melting  it  with  a  little  anti- 
mony. The  residual  slag  -yields  its  antimony  to  hydrofluoric 
acid,  from  which  solution  it  may  be  deposited  electrolytically 
as  described  in  Chapter  III.  About  one-half  the  copper  pres- 
ent also  dissolves  in  the  HF,  the  removal  of  which  will  be 
taken  up  with  the  description  of  antimony  depositing. 

Dilute  nitric  acid  was  tried  for  dissolving  lead  and  bis- 
muth from  the  slag,  after  which  the  residue  could  be  con- 
verted into  antimony  or  antimony  compounds.  If  the  nitric 
acid  is  not  very  strong  little  or  none  of  the  antimony  is  con- 
verted to  higher  oxides,  as  it  is  difficult  to  peroxidize  it. 
Nitric  acid  acts  slowly  on  the  slag,  finally  leaving  a  soft  light 
yellow,  rather  dense  residue  of  antimony  oxide  and  a  solu- 
tion of  lead  nitrate,  which  can  be  easily  crystallized. 

Mattes  high  in  silver  are  analogous  to  the  sulphides  made 
from  silver  ores  in  a  hyposulphite  leaching  mill.  There  are 
several  methods  for  treating  such  material.  Stetefeldt's 
process  of  melting  the  sulphides  in  an  iron  pot,  roasting,  and 
dissolving  out  copper  sulphate  with  water  in  presence  of 
metallic  copper  to  precipitate  any  silver  in  solution,  would 
seem  to  be  applicable  to  the  present  material  from  the  roast- 
ing stage  on.  The  residue  from  the  copper  extraction  con- 
sists mainly  of  silver.  The  roasting  was,  as  described  by 
Stetefeldt,  performed  in  a  small  muffle-furnace  after  being 
first  ground  in  a  small  ball-mill.  Details  will  be  found  in 


78  LEAD  REFINING  BY  ELECTROLYSIS. 

Stetefeldt's,  "  The  Lixiviation  of  Silver  Ores  with  Hyposul- 
phite Solutions,"  and  Collins'  "  Metallurgy  of  Silver." 

The  sulphuric  acid  process  (Dewey-Walter  process)  con- 
sists in  boiling  the  sulphides  with  hot  concentrated  sulphuric 
acid  in  an  iron  pot.  The  sulphuric  acid  oxidizes  the  sulphur 
of  the  sulphides  as  well  as  the  metals.  It  seems  reasonable 
to  suppose  that  the  matte,  if  ground  fine,  would  react  simi- 
larly to  precipitated  sulphides.  If  so,  this  method  would  be 
much  simpler  and  cheaper  than  the  roasting  method.  Details 
will  be  found  in  Collins'  "  Metallurgy  of  Silver." 

I  have  found  that  these  mattes  are  as  readily  converted 
to  bullion  by  the  following  process:  Grind  the  matte,  and 
add  in  an  iron  pot  enough  concentrated  sulphuric  acid  to 
react  with  all  the  silver  and  copper  as  follows: 

Ag2S  +  2H2S04  -  2Ag  +  3S02  +  2H20, 
Cu2S  +  2H2S04 = 2Cu  +  3S02  +  2H20. 

On  heating  the  mixture  gently  part  of  the  matte  is  con- 
verted to  sulphates,  and  a  little  sulphur  comes  off  with  much 
S02.  The  dry  product  is  transferred  to  a  melting  crucible, 
and  treated,  when  the  mass  melts  down  quietly,  to  copper- 
silver  bullion. 

Melting  with  the  addition  of  sulphur  for  matte  and  slag. — 
In  case  the  slime  contains  little  bismuth,  or  only  small  quan- 
tities of  silver,  the  direct  fusion  of  the  partially-oxidized  slime 
suffers  from  two  disadvantages.  One  is  the  high  tempera- 
ture necessary  to  melt  the  dore  bullion,  which  is  too  high 
for  antimony  trioxide  to  remain  as  liquid,  and  on  the  other 
hand,  either  the  silver  is  apt  to  go  into  the  slag,  or  the  dore* 
contains  too  much  Lead  and  antimony. 


CHEMISTRY  OF  SLIME  TREATMENT.  79 

A  very  neat  melting  method  consists  in  adding  sulphur 
to  the  air-oxidized  slime,  in  about  sufficient  quantity  to 
reduce  any  Sb205  to  Sb203  and  to  form  a  silver-copper  matte 
with  the  copper  and  silver  of  the  slime.* 

As  an  example  Trail  slime  containing,  when  dried, 

Ag 14.6% 

Cu 8.1% 

Sb 27.60% 

Pb 16.0% 

As 27.0% 

Au 34  ozs.  per  ton. 

was  melted  with  various  amounts  of  sulphur  from  8  to  12%. 
8%  was  found  to  be  about  right.  rWhen  the  slime  was  given 
a  slight  further  roast  as  a  preliminary,  a  little  more  sulphur 
was  used. 

100  grams  roasted  slime  and  10  grams  sulphur,  melted  in 
a  porcelain  crucible,  gave 

TABLE  32. 

Matte,  43  Gr.  Slag,  45  Gr. 

Ag 34.0%  Cu 0.2% 

Cu 19.2%  Pb 12.1% 

Pb 24.8%  Sb 51.4% 

S 13.9%  As 5.2% 

Au 25%  Fe 3.0% 

Sb 5.8% 

Other  mattes  from  the  same  slime  contained: 

TABLE  33. 

Ag 41.7%  38.1%  46.8% 

Cu 23.2%  21.8%  26.3% 

Pb 17.5%  5.8% 

*  Patent  applied  for. 


80  LEAD  REFINING  BY  ELECTROLYSIS. 

100  grams  of  the  unroasted  but  thoroughly  oxidized  slime 
gave  with  7  grams  of  sulphur  35  grams  of  matte  and  46  grams 
of  slag.  This  matte  contained  less  lead  (about  5%)  and  less 
antimony. 

The  melting  temperature  was  low,  about  600°  C.  The 
matte  should  have  no  action  on  iron,  and  the  slag  might  not 
either,  so  I  tried  a  cast-iron  pot  for  melting. 

400  grams  of  slime  and  28  grams  of  sulphur  were  added 
to  the  red-hot  pot,  and  melted  down.  Large  quantities  of 
arsenic  came  off.  The  product  consisted  of  140  grams  of 
matte  with  considerable  metal  intermixed,  and  about  190 
grams  of  slag. 

Another  melt  with  32  grams  sulphur  gave  a  product  with 
no  metal,  but  the  cast  was  spoiled,  and  the  products  melted 
over  again,  with  the  addition  of  a  few  grams  of  sulphur. 
Products  were  about  160  grams  matte  and  165  grams  slag. 

After  these  three  melts  the  pot  shows  no  sign  of  wear. 
The  last  slag,  however,  analyzed  8.25%  iron  as  against  3% 
when  melted  without  access  of  iron.  On  the  other  hand, 
the  fusion  in  an  iron  crucible  gave  a  slag  lower  in  silica,  as  of 
course  would  be  expected. 

Treatment  of  the  slag:  (1)  This  has  been  reduced  to 
hard  lead  by  smelting  with  litharge  and  carbon,  from  which 
first  the  lead  may  be  extracted  electrolytically,  see  page 
5:,  and  the  antimony  residue  refined  with  the  fluoride  so- 
lution. 

(2)  It  can  be  leached,  after  grinding,  with  hydrofluoric 
acid  for  antimony  fluoride  solution.  The  action  of  hydro- 
fluoric acid  is  rapid  and  evolves  considerable  heat.  The  anti- 
mony can  be  deposited  from  the  fluoride  solution,  to  which 
sulphuric  acid  should  be  added.  If  the  hydrofluoric  acid 


CHEMISTRY  OF  SLIME  TREATMENT.  81 

used    contain    also    sulphuric    acid,   the    residue  will   consist 
mostly  of  lead  sulphate. 

(3)  The   slag   may   also   be   leached    after    grinding    with 
dilute   nitric    acid.     After   several   hours'    action   the   residue 
consists  of  yellow  antimony  trioxide  and  the  solution  con- 
tains lead  nitrate.     The  production  of  lead  nitrate  as  a  by- 
product of  a  lead  refinery  is  analagous  to  the  production  of 
copper  sulphate  by  a  copper  refinery. 

(4)  The    slag    can    be    reduced   to    metal    electrolytically, 
either  with  a  fused  electrolyte  as  lead  chloride,  see  page  66, 
or  with   an   aqueous   electrolyte,   as   sulphuric   acid   solution. 
The  following  experiment  illustrates  the  latter: 

100  grams  of  slag  containing  about  50%  antimony,  8% 
iron,  5%  arsenic,  and  15%  lead,  were  ground  rather  fine,  say 
30  mesh,  and  placed  in  a  shallow  lead  pan  about  3  by  4  inches 
and  about  1  inch  deep.  25%  sulphuric  acid  was  added  and 
a  horizontal  lead  anode  used  about  2J  by  3J  inches,  wrapped 
in  cloth  and  about  J  inch  from  the  slag.  The  current  varied 
from  three  to  six  amperes,  equivalent  to  a  current  density 
40-80  amperes  per  square  foot.  During  most  of  the  run 
no  gas  was  seen  to  rise  from  the  cathode.  About  the  middle 
of  the  run  red  antimony  sulphide  appeared  in  the  electrolyte 
and  floated  around,  the  total  quantity  produced  being  2.45 
grams.  Current  necessary  for  complete  reduction  about 
38  ampere  hours,  and  when  36  ampere  hours  had  passed  H2S 
came  off  for  a  while,  and  then  was  replaced  by  hydrogen. 
The  appearance  of  H2S  would  be  a  good  indication  of  the  end 
of  the  reaction. 

Any  iron  of  course  went  into  solution  as  ferrous  sulphate. 
It  was  thought  that  fluorine  and  silica  might  both  be  present 
in  the  slag  and  give  rise  to  the  formation  of  H2SiF6  during 


82 


LEAD  REFINING   BY   ELECTROLYSIS. 


the  action.  Acids  forming  soluble  lead  salts  cause  a  rapid 
corrosion  of  lead  anodes  in  sulphuric  acid,  so  I  rather  expected 
lead  sulphate  would  drop  off  the  anodes  into  the  slag  during 
the  run,  and  used  a  cloth  to  keep  any  from  dropping  into  the 
slag.  The  lead  anode,  however,  was  not  attacked. 

The  cathode  area  was  10-12  square  inches;  anode  area, 
8.9  square  inches;  current  3-6  amperes,  e.m.f.  2.25  to  2.9 
volts. 

TABLE  34. 


Time, 
Hrs.  Min. 

Volts. 

Amperes. 

Amperes, 
Hours. 

Remarks. 

0.15 
0.30 
2.30 
2.45 
5.35 
9.28 
9  58 

2.25 
2.25 
2.25 
2.45 
2.50 
2.60 
2  60 

4.3 
3.5 
3.5 
3.0 
3.5 
3.0 
3  2 

'9.S5 
31.67 

31.25 

No  gas  noticed  coming  from  cathode. 
No  gas  noticed  coming  from  cathode. 
No  gas  noticed  coming  from  cathode. 
No  gas  noticed  coming  from  cathode. 
No  gas  noticed  coming  from  cathode. 
Sb^  suspended  in  electrolyte. 
SboSo  suspended  in  electrolyte 

10  45 

2  6 

3  2 

Some  HgS  evolved 

11.35 
12.20 
12.45 
13.45 
15.05 
16.25 
17.05 

2.75 
2.65 
2.65 
2.9 
2.7 
2.8 

4.6 
5.8 
5.0 
5 
3.6 
3.5 

44.93 
55 

No  H2S  evolved. 

The  rise  in  voltage  after  about  12  hours  and  45  minutes 
indicated  the  completion  of  the  reaction. 

The  electrolyte  contained  some  ferrous  sulphate.  Part  of 
the  former  slag  was  cemented  to  the  lead  tray  and  part  was 
loose.  It  had  not  changed  much  in  appearance. 

After  washing,  and  before  drying,  part  of  the  product 
was  rapidly  melted  in  a  crucible,  producing  metal  and  no  slag, 
showing  good  reduction.  Another  test  was  made  and  gave 
15.5  gr.  metal  and  4.5  gr.  slag.  In  the  first  test  a  clay  cruci- 


CHEMISTRY  OF  SLIME  TREATMENT.  83 

ble  was  used  which  probably  had  absorbed  the  small  quan- 
tity of  slag. 

To  reduce  the  40-45  grams  antimony  and  15  grams  lead 
in  the  slag  would  require  about  40  ampere  hours,  which  it 
will  be  noticed  corresponds  with  the  increase  in  voltage.  The 
current  efficiency  appears  from  the  slight  evolution  of  hydrogen 
and  from  the  above  noted  circumstances,  to  be  quite  high. 
The  slag  produced  in  melting  may  have  resulted  from  oxi- 
dation during  drying  and  fusion. 

These  slags  may  also  be  conveniently  reduced  to  hard 
lead,  by  smelting  with  litharge  or  dross  from  the  refined  lead 
pot  and  carbon. 

The  extraction  of  the  lead  from  the  hard  lead  is  achieved 
by  refining  with  the  fluosilicate  electrolyte.  Further  experi- 
ments are  necessary  before  it  is  possible  to  say  whether  it 
would  be  better  to  melt  the  antimony  residue  and  refine  elec- 
trolytically  with  the  fluoride  solution,,  or  refine  the  antimony 
skeleton  directly  as  anode  in  the  same  solution. 

Direct  electrolysis  with  slime  as  anode. — As  the  slime 
retains  very  often  the  form  of  the  original  anode,  especially 
when  the  percentage  of  impurity  is  rather  high,  say  3  to  10%, 
the  proposition  of  placing  the  anode  with  the  slime  still  adher- 
ing in  an  appropriate  solution,  and  making  it  the  anode, 
while  one  of  the  principal  metals  contained  goes  over  to  the 
cathode,  seems  promising. 

Some  means  of  removing  or  washing  out  the  lead  electro- 
lyte in  the  slime,  worth  on  the  average,  say  $2.25  per  ton 
of  lead  refined,  is  very  necessary.  In  time,  with  frequent 
changes  of  wash-water  in  a  tank  containing  a  set  of  anodes, 
this  solution  could  be  removed  to  any  desired  extent  by  the 
simple  action  of  diffusion.  We  tried  another  method,  namely, 


84 


LEAD  REFINING  BY  ELECTROLYSIS. 


connecting  up  the  anode  with  attached  slime  as  cathode  in 
a  solution  of  fluosilic  acid,  with  carbon  anodes.  Passing  the 
current  deposits  some  lead  in  and  on  the  slime,  and  lead 
peroxide  on  the  anode,  while  the  valuable  SiF6  present  of 
course  moves  away  from  the  slime,  now  cathode,  into  the 
solution.  A  removal  is  possible  in  this  way,  but  our  result 
from  the  following  experiment  could  not  be  called  successful. 

The  original  lead  alloy  contained  lead  90%;  arsenic  5%; 
antimony  3.0%;  copper  1%;  silver  0.7%,  and  Bi  0.05%,  and 
was  refined  with  an  electrolyte  containing  8.05  grams  lead 
and  15.9  grams  SiF6  per  100  cc.  The  anode  was  originally 
about  I"  thick,  and  was  treated  until  the  lead  was  practi- 
cally all  removed. 

The  residue  was  then  made  cathode  in  a  solution  contain- 
ing 6.15  grams  SiFe  per  100  cc.  and  no  lead.  Volume  of  solu- 
tion 715  cc.=46.5  gr.  SiFg.  Anodes  of  carbon  (}"  round 
electric  light  carbons). 

TABLE  35. 


Time. 

Amperes  . 

Volts. 

Amperes 
per  Square  Foot. 

Temperature. 

9.30 

1.82 

2.45 

12.5 

16°  C. 

9.45 

1.82 

2.40 

12.5 

10.20 

1.45 

2.25 

9.9 

17°  C. 

11.30 

1.93 

2.40 

13.2 

19°  C. 

4.00 

1.45 

2.40 

9.9 

20°  C. 

The  SiF6  in  the  solution  increased  by  only  8.5  grams 
instead  of  10.7  grams  or  more  present  in  the  slime. 

The  volume  of  the  pores  in  the  slime  treated  was  67  cc. 
While  sufficient  current  was  passed  to  remove  29.1  SiFe  grams 
at  100%  efficiency,  only  part  of  that  present  was  actually 
removed,  with  an  efficiency  of  about  30%. 


CHEMISTRY  OF  SLIME  TREATMENT. 


85 


It  is  possible  to  so  choose  the  electrolyte  for  refining  the 
attached  slime,  that  the  fluosilicic  acid  and  lead  fluosilicate 
of  the  slime  is  not  lost,  but  may  be  recovered  from  the  second 
electrolyte. 


o 


1.75 


1.50 


1.25 


1.00 


.75 


.50 


,25 


9  10 

Time  Hours 
FIG.  10. 


11 


EXPERIMENT. — Bullion  containing  arsenic  5%,  antimony 
3%,  and  copper  1%  in  the  shape  of  an  anode,  SiXliX 
if  inches,  was  electrolyzed  until  300  grams  lead  was  dissolved 
out,  or  about  350  grams  of  alloy  decomposed.  The  core  was 
then  about  f"  thick.  The  slime  was  scraped  off  one  side  for 


86  LEAD  REFINING  BY  ELECTROLYSIS. 

another  experiment  and  the  other  half  made  anode  in  a  hot 
solution  containing  15%  CuS04-5H20  and  H2S04.  Tem- 
perature about  70°  C.  On  the  start  with  a  current  of  1  ampere 
the  voltage  was  .26,  rising  after  about  six  hours  as  plotted 
in  Fig.  10.  The  copper  deposited  remained  good,  though 
the  voltage  finally  increased  very  much.  A  small  quantity 
of  Sb20s  was  found  in  the  solution,  but  nearly  all  remained 
in  the  slime,  with  some  lead  sulphate. 

Of  course  the  concentration  of  copper  in  the  solution 
continually  got  smaller,  for  little  was  supplied  by  the  anode 
to  make  up  for  that  deposited  at  the  cathode,  the  result  of 
the  electrolysis  being  expressed  by  these  reactions: 

3CuS04  +  2Sb  =  3Cu  +  Sb203  +  3H2S04  ; 
3CuS04  +  2As  =  3Cu  +  As203  +  3H2S04  ; 
CuS04  +  2Ag=  Cu+Ag2S04. 


The  peculiar  flat  place  in  the  curve  corresponds  in  volt- 
age to  the  formation  of  silver  sulphate  in  the  slime,  and  may 
be  due  to  silver  dissolving  at  that  time. 

Twelve  grams  of  copper  were  deposited,  about  9.5  before 
voltage  reached  .4  volt  and  2.5  grams  thereafter.  Roughly 
there  were  in  the  slime  7.5  grams  arsenic,  6  grams  antimony, 
and  1.5  grams  copper,  equivalent  to  the  deposition  of  16.0 
grams  of  copper,  so  that  the  oxidizing  efficiency  at  the  anode 
was  about  75%. 

The  anode,  with  the  slime  still  remaining  on  it,  was  put 
in  dilute  HF+H2S04,  with  the  idea  that  the  antimony  would 
dissolve  out  and  the  slime  drop  off,  which  would  be  a  good 
thing  in  practice  as  it  would  save  cleaning  the  anode  scrap. 
However,  the  slime  did  not  fall  off,  perhaps  because  the  HF 


CHEMISTRY  OF  SLIME  TREATMENT.  87 

used  was  too  small  in  quantity,  theoretically  only  just  about 
sufficient  being  used  to  form  SbF3,  while  an  excess  should  have 
been  used  on  account  of  the  long  time  necessary  to  complete 
the  reaction. 

To  make  use  of  this  simple  process  the  following  condi- 
tions are  necessary: 

(1)  Anodes  containing  enough  impurity  to  cause  the  slime 
to  hold  together  quite  firmly.  (2)  Rather  thin  anodes,  in 
order  that  the  electrolytic  action  can  penetrate  all  the  slime. 
(3)  A  supply  of  copper  sulphate,  or  copper  containing  mate- 
rial, as  matte,  which  could  be  treated  with  the  dilute  sul- 
phuric acid  produced  in  the  process  to  make  copper  sulphate 
solution.  (4)  Recovery  of  H2SiF6  from  the  copper  sulphate 
sulphuric  acid  solution,  as  by  precipitation  with  K2S04,  and 
distillation  of  the  sodium  fluosilicate  with  sulphuric  acid  to 
recover  H2SiF6. 

The  arsenic  of  course  dissolves  in  the  hot  solution  and 
can  be  crystallized  out  merely  by  cooling.  Analysis  of  the 
figures  noted  in  the  experiment  indicate  that  the  electrolysis 
goes  smoothly,  as  long  as  metallic  arsenic  remains  in  the 
slime,  and  thereafter  the  voltage  rises. 

The  recovery  of  antimony  and  hydrofluoric  acid  would 
be  by  the  usual  method  described  in  Chapter  III. 

Such  a  slime  process  can  be  carried  out  with  other  solu- 
tions than  that  of  copper  sulphate  and  sulphuric  acid;  for 
example,  antimony  or  copper  fluoride-hydrofluoric  acid  solu- 
tion which  possesses  the  advantage  of  taking  nearly  the 
entire  slime;  that  is,  the  arsenic,  antimony,  and  copper  into 
solution,  while  depositing  copper  at  the  cathode. 

In  refining  bullion  containing  Pb  65.37%,  Bi  7.32%,  Sb 
19.51%,  As  5.85%,  and  Ag  1.95%,  an  anode  covered  with 


LEAD  REFINING  BY  ELECTROLYSIS. 


slime  was  electrolyzed  in  a  solution  of  SbF3  +  HF  +  Na2S04r 
containing  about  4%  antimony.  The  cathode  deposit  was 
black  and  spongy  and  the  e.m.f.  very  high,  so  that  it  was 
not  a  success.  This  may  be  due  to  the  fact  that  the  solution 
contained  SO/',  which  I  afterward  found  out  was  a  mis- 
take. When  S04"  is  present  the  antimony  is  converted  at 
the  anode  partly  into  insoluble  basic  insulating  compounds, 
while  if  the  only  anion  present  in  F',  the  antimony  goes 
straight  into  solution  as  SbFs. 

An  alloy  containing  Pb  65.56%,  Ag  1.94%,  Cu  1.94%,  Bi 
6.84%,  As  5.47%,  and  Sb  18.24%,  after  removing  the  lead 
electrolytically,  was  treated  in  the  same  way,  only  all  PbSiF6 
was  removed  by  steeping  the  anode,  after  extracting  lead, 
in  hot  water.  The  antimony  electrolyte  contained  6.4  grams 
Sb,  as  SbF3,  5.4  grams  HF  and  5  grams  (NH4)2S04  per  100  cc, 

The  results  are  given  in  Table  36. 


TABLE  36. 


Back 

Time. 

Amperes. 

Volts. 

Amperes, 
Sq.  Ft. 

E.M.F. 
Volts. 

Remarks  . 

0.5  hours 

0.36 

0.42 

6.7 

0.23 

5.0 

0.38 

0.38 

6.1 

0.14 

8.0 

0.34 

0.38 

5.4 

0.14 

Fair  deposit. 

14.1 

0.29 

0.34 

4.6 

0.15 

17-  1 

0.33 

0.38 

5.3 

0.18 

17.1 

0.33 

0.36 

5.3 

0.18 

26.  | 

0.28 

0.38 

4.5 

0.18 

Fair  deposit. 

136 

0.10 

1.24 

1.6 



Powdery  deposit. 

The  slime  was  irregularly  attacked,  being  very  hard  in 
places  and  very  soft  in  others.  The  core  had  been  attacked 
seriously  under  the  soft  spots,  showing  the  current  was 
applied  for  too  long  a  time. 


CHEMISTRY  OF  SLIME  TREATMENT.  89 

Fusion  to  alloys  and  electrolytic  refining. — In  the  para- 
graph on  "  fusion",  page  64,  a  description  is  given  of  an 
easy  method  of  eliminating  lead  from  the  alloy  if  desired. 
It  is  then  possible  to  eliminate  lead  in  the  first  place,  so  if 
the  presence  of  lead  is  objectionable  on  account  of  any  elec- 
trolytic process  desired  to  be  used,  it  may  be  disposed  of  on 
the  start. 

The  treatment  of  the  alloy  by  electrolysis  will  of  course 
depend  on  the  composition  of  the  alloy.  If  it  should  be 
mostly  bismuth,  as  it  might  be  in  working  up  bismuth  alloys, 
it  could  be  electrolytically  refined  with  a  solution  contain- 
ing about  10%  free  methylsulphuric  acid  and  4%  of  bismuth 
as  methylsulphate.  This  makes  an  excellent  electrolyte  for 
refining  bismuth.*  If  the  alloy  is  mainly  silver,  copper,  or 
antimony,  refining  with  the  solution  appropriate  for  that 
metal  could  be  adopted. 

For  the  usual  case,  producing  a  mixed  alloy  with  rela- 
tively large  amounts  of  silver  and  antimony  and  important 
amounts  of  lead,  copper  and  perhaps  bismuth,  this  method 
does  not  seem  to  offer  sufficient  advantages  over  the  usual 
wet  methods  of  treatment.  In  this  case  it  would  be  advisable 
to  add  outside  antimony,  silver,  or  copper  that  would  be 
refined  anyway,  to  make  a  preponderating  proportion  of  one 
metal,  which  is  always  desirable  in  electrolytic  refining.  Of 
the  three  metals  copper  offers  the  chief  advantages.  Copper 
for  refining  is  usually  available,  it  produces  the  most  satis- 
factory cathode  deposit,  and  comes  down  as  pure  metal, 
and  most  important  of  all  the  resulting  slime  was  found  to 

*  According  to  Mohn,  bismuth  trichloride,  with  10%  free  HC1,  is  used 
successfully  for  this  purpose.  Electrochemical  and  Metallurgical  Industry, 
August,  1907. 


90  LEAD  REFINING  BY  ELECTROLYSIS. 

contain  only  traces  of  copper  or  antimony,  and  thus  a  sharp 
separation  and  complete  recovery  of  the  metals  is  easy. 
There  is  no  difficulty  in  depositing  pure  copper  in  presence 
of  antimony  fluoride,  even  though  the  percentage  of  copper 
falls  to  a  very  low  figure,  if  a  brisk  circulation  is  kept  up. 
This  then  affords  a  separation,  copper  on  the  cathodes,  anti- 
mony collects  on  the  solution  and  continually  increases  in 
amount  while  copper  diminishes,  and  silver,  bismuth,  and 
gold  constitute  the  slime. 

In  one  experiment  the  alloy,  which  contained  approxi- 
mately 30%  silver,  45%  antimony,  14%  bismuth,  and  9% 
copper,  was  melted  in  a  crucible  and  two  and  one-half  times 
its  weight  of  copper  added,  under  a  cover  of  salt,  and  then 
contained  8.6%  silver,  12.9%  antimony,  4%  bismuth,  74% 
copper.  There  was  no  volatilization  during  the  process,  and 
the  alloy  was  very  much  more  readily  fusible  than  copper. 
The  maximum  temperature  during  the  melt  did  not  exceed 
800°  C.  probably. 

The  alloy  was  electrolytically  refined  with  a  solution 
containing  CuF2,  NaF,  and  HF,  and  no  H2S04.  Copper 
was  deposited  in  a  satisfactory  condition  on  the  cathodes, 
though  it  was  not  as  solid  as  the  copper  from  a  sulphate  solu- 
tion. The  cathodes  were  bright  and  clean  looking,  but  the 
crystallization  was  coarser  than  is  obtained  with  a  sulphate 
solution. 

Some  white  bismuth  compound  separated  on  the  bottom 
of  the  tank  during  electrolysis,  and  the  anode  slime  contained 
the  remainder  of  the  bismuth,  as  well  as  the  silver,  and  1% 
copper  and  2.5%  of  antimony.  The  extraction  of  antimony 
and  copper  was  then  approximately  96%  and  99.7%  of  that 
present  respectively.  The  slime  would  be  melted  for  dor6 


CHEMISTRY  OF  SLIME  TREATMENT.  91 

bullion  and  a  bismuth  slag,  and  the  solution,  which  continu- 
ally diminishes  in  copper  content  while  antimony  increases, 
would  have  to  be  treated  for  metallic  antimony  and  regener- 
ation of  the  copper  fluoride;  for  example,  by  precipitating  the 
remaining  copper  by  running  the  solution  through  broken 
antimony,  depositing  antimony  from  the  solution  with  a 
lead  anode  and  neutralizing  HF  in  the  solution  with  copper 
oxide,  roasted  matte,  etc. 

Wet  treatment  with  regeneration  of  the  solutions.  —  By 
getting  the  metals  of  the  slime  into  the  solution  in  some  way 
and  electrolyzing  the  solution  for  the  contained  metals,  and 
simultaneously  producing  an  anode  product  which  may  be 
used  in  oxidizing  further  quantities  of  slime,  important  advan- 
tages may  be  secured.  It  not  being  necessary  to  dry  the 
slime,  the  danger  of  loss  from  dutsing  and  the  physical  discom- 
fort of  working  with  such  poisonous,  penetrating  dust,  are 
avoided,  as  well  as  the  involved  expense.  For  any  wet  treat- 
ment process  the  raw  slime  is  better  suited  than  it  is  after 
drying  on  account  of  its  more  open  nature.  The  chemicals 
required,  an  imporant  item  in  most  methods,  are  reduced 
in  amount,  only  enough  being  required  to  make  up  for 
mechanical  losses.  A  certain  amount  of  electric  energy  is 
needed,  but  this  is  not  great.  It  will  be  noticed  that  in 
most  of  the  other  methods  outlined,  steps  are  introduced 
which  require  electric  energy,  so  this  item  applies  to  prac- 
tically all  methods  anyway,  and  is  not  therefore  a  disadvant- 
age peculiar  to  this  class  of  processes. 

The  acids,  the  salts  of  which  have  been  used  in  the  solu- 
tions, are  few  in  number,  the  choice  being  necessarily  limited. 
The  ideal  acid  to  use  is  the  same  as  that  used  in  the  lead 
depositing  electrolyte,  that  is,  fluosilicic  acid.  A  combina- 


92  LEAD  REFINING  BY  ELECTROLYSIS. 

tion  of  lead  peroxide  as  oxidizing  agent  and  fluosilicic  acid 
solution  has  an  important  advantage  on  the  score  of  sim- 
plicity of  the  whole.  With  their  use  it  would  not  be  neces- 
sary even  to  wash  the  slime,  as  the  two  electrolytes,  slime 
treating  and  lead  depositing,  are  the  same,  and  after  suitable 
purification  of  the  slime  electrolyte  can  be  exchanged  when 
convenient. 

With  the  fluosilicate  electrolyte  we  may  use  lead  per- 
oxide as  oxygen-carrier,  and  the  other  metal  that  has  been 
used  as  oxygen  carriers  from  the  anode  to  the  slime  is  iron, 
passing  from  the  ferrous  to  the  ferric  state,  and  back  again. 

The  production  of  ferric  fluosilicate  has  not  been  seri- 
ously attempted,  and  there  are  certain  objections  to  its  use. 
One  comes  from  the  fact  that  in  electrolyzing  the  solution 
with  insoluble  anodes  of  carbon  for  ferric  fluosilicate,  silica 
deposits  on  the  anodes  and  stops  the  oxidation  of  the  iron, 
while  if  hydrofluoric  acid,  in  small  quntity,  is  used  to  pre- 
vent this,  the  difficulties  in  the  way  of  a  successful  diaphragm, 
materials  containing  silica  being  barred,  have  prevented  any 
serious  attempt  in  this  line. 

Fluosilicic  acid  being  unsuitable,  we  find  that  sulphuric, 
hydrochloric,  and  hydrofluoric  acids  are  cheap  enough  to  be 
considered  from  slime-treating  solutions.  The  question  of 
tanks  is  an  important  one,  on  which  depends  to  a  large 
extent  the  choice  of  available  acids.  Until  recently,  there 
appeared  to  be  no  suitable  tank  for  working  with  strongly 
acid  chloride  solutions  (to  keep  SbClg  from  decomposing). 
However,  a  concrete  tank,  saturated  with  sulphur,  described 
in  Chapter  VII,  is  not  acted  on  by  hydrochloric  acid. 

Ferric  chloride  has  been  used  in  experiments  on  anti- 
mony slime  from  refining  hard  lead.  The  electrolyzed  solu- 


CHEMISTRY  OF  SLIME  TREATMENT.  93 

tion  contained  beside  hydrochloric  ferrous  chloride  and  anti- 
mony trichloride,  which  yielded  antimony  on  the  cathode 
and  ferric  chloride  at  the  anode.* 

Ferric  sulphate  is  an  ideal  solution  in  some  ways,  on  ac- 
count of  the  cheapness  with  which  it  may  be  produced  and 
the  ease  of  handling  it  in  lead-lined  tanks.  It  also  has  an 
advantage  in  separating  copper  and  arsenic  in  solution,  from 
antimony  hydroxide  and  silver  in  the  undissolved  portion. 

Hydrofluoric  acid  may  also  serve  as  a  basis  of  the  solu- 
tion, and  ferric  fluoride  be  formed  at  the  anode  as  oxidizer. 
Hydrofluoric  acid  may  also  be  used  in  connection  with  ferric 
sulphate,  when  the  antimony  will  go  into  solution  as  anti- 
mony trifluoride. 

The  use  of  the  insoluble  anode  product,  lead  peroxide,  has 
also  been  tried.  Lead  peroxide  is  easily  obtained  in  quan- 
tity in  dense  scales  and  plates  by  electrolyzing  lead  fluosili- 
cate  solution  with  a  graphite  anode. 

Lead  peroxide  and  metallic  lead,  copper,  etc.,  in  slime 
react  with  lead  peroxide  in  the  presence  of  fluosilicic  acid, 
for  instance,  to  form  fluosilicates. 

Pb  +  Pb02 + 2H2SiF6  -  2PbSiF6  +  2H20. 

Ferric  sulphate  process. — This  is  a  neat  process,  and  has 
been  the  subject  of  a  great  deal  of  experimenting.  It  is 
applicable  to  slime  from  copper  refining  as  well  as  to  lead 
slime.  In  the  treatment  of  copper  refinery  slime  it  is  apt  to 
find  a  large  use.  The  description  may  also  prove  of  interest 
in  connection  with  the  Siemens  &  Halske  process  for  copper 
ores  and  matte,  f 

*  A.  G.  Betts,  Trans.  Am.  Electrochemical  Society,  Vol.  VIII,  page  188. 
t  Borcher;s  "Electric  Smelting  and  Refining."     2d.  Eng.  Ed.,  page  260. 


94  LEAD  REFINING  BY  ELECTROLYSIS. 

Ferric  sulphate  is  a  very  soluble  salt,  of  which  a  syrupy 
solution  containing  10%  Fe"  may  be  readily  prepared.  This 
is  too  strong  for  work  with  slime,  principally  on  account  of 
the  less  solubility  of  the  resulting  ferrous  sulphate.  Solutions 
used  for  slime  treating  should  contain  about  five  volume  per 
cent  of  iron. 

Ferric  sulphate  solution  reacts  with  slime  very  readily, 
oxidizing  metallic  copper  and  cuprous  sulphide  to  copper 
sulphate,  antimony  to  hydrated  trioxide,  arsenic  to  arsenious 
acid,  bismuth  to  basic  sulphate,  finely-divided  lead  to  lead 
sulphate,  and  when  hot  converts  silver  to  silver  sulphate. 
The  complete  oxidation  of  silver  is  difficult  or  impossible  on 
account  of  the  reducing  action  of  the  ferrous  sulphate 
formed.  Practically,  to  dissolve  one-half  to  two-thirds  of 
the  silver  in  slime  requires  the  use  of  a  considerable  excess 
of  ferric  sulphate,  so  that  the  process  is  simplified  in  some 
respects  by  only  using  enough  ferric  sulphate  to  oxidize  the 
other  metals.  When  slime  contains  sulphur  or  sulphides, 
which  it  almost  always  does,  especially  copper  slime,  the  solu- 
tion of  silver  is  hindered  or  entirely  prevented.  Apparently 
in  the  reaction  between  ferric  sulphate  and  silver  little  or 
no  energy  is  liberated  and  the  presence  of  finely-divided  sul- 
phur, combining  with  the  silver,  can  even  reverse  the  action 
giving 


Tellurium  is  dissolved  by  ferric  sulphate  and  may  be  pre- 
cipitated out  on  metallic  copper,  as  a  greasy,  black  coating. 
Selenium  and  gold  are  not  dissolved  from  slime  by  ferric  sul- 
phate. 


CHEMISTRY  OF  SLIME  TREATMENT.  95 

As  the  solution  is  prepared  by  electrolysis,  and  it  is  ad- 
visable to  have  a  solution  of  as  high  conductivity  as  possible , 
the  ferric  sulphate  used  will  contain  some  free  sulphuric 
acid,  2-5%,  and  some  ferrous  sulphate,  usually  equivalent 
to  1%  ferrous  iron,  Fe". 

From  the  reactions  taking  place,  it  will  be  seen  that  the 
process  is  not  entirely  cyclic.  The  reaction  of  the  copper 
of  the  slime,  Cu  +  Fe2(S04)3  =  CuS04H-2FeS04,  is  directly 
reversed  in  the  electrolytic  tank,  so,  as  far  as  copper  is  con- 
cerned, the  same  solution  could  be  used  over  and  over  again 
without  any  additions  being  made  to  it.  In  treating  copper 
slime,  consisting  largely  of  Cu2S  and  silver,  this  condition 
is  quite  well  realized. 

The  reaction  on  antimony  and  arsenic,  which  consumes 
a  good  percentage  of  the  ferric  iron  used,  is  not  reversible. 
Oxygen  is  removed  from  the  solution  in  the  insoluble  anti- 
mony hydrate,  and  arsenic  removes  oxygen  from  the  cycle 
though  not  from  the  solution.  Lead  removes  SO/',  but  not 
in  large  or  serious  quantity. 

For  many  slimes,  containing  say  30%  Sb,  15%  Cu,  10%  As, 
beside  lead  and  silver,  the  amount  of  iron  reduced  by  anti- 
mony and  arsenic  would  approximate  two-thirds  of  the  total. 

Several  methods  exist  of  adding  combined  oxygen  to  the 
solution  to  make  up  the  deficiency, .  but  the  best  seems  to  be 
the  addition  of  copper  oxide  in  some  form,  especially  as  roasted 
copper  or  copper-lead  matte.  As  the  copper  is  recovered  as 
electrolytic  metal,  from  a  raw  material,  the  process  may  be 
credited  with  part  of  the  enhanced  value  of  the  copper.  With 
the  addition  of  copper  oxide  from  any  source,  and  crystalli- 
zation from  the  solution  of  arsenious  acid,  the  solution  may 
be  used  over,  if  mechanical  losses  are  made  up. 


96  LEAD  REFINING  BY  ELECTROLYSIS. 

Another  method  of  supplying  oxygen  consists  in  air-dry- 
ing the  slime  before  treatment  with  ferric  sulphate,  which 
introduces  considerable  oxygen,  but  this  suffers  from  several 
objections,  such  as  the  formation  of  hard  lumps  which  are 
attached  with  difficulty  and  greater  expense  and  losses. 

The  separation  of  the  metals  by  the  sulphate  solution  is 
not  perfect,  principally  because  antimony  and  bismuth  hy- 
droxides or  basic  salts  are  not  entirely  insoluble  in  the  solu- 
tion. The  solubility  of  Sb203  in  the  solution  is  approximately 
1.6  grams  per  litre  cold  and  2.2  grams  hot.  Variations  in 
the  percentage  of  sulphuric  acid  have  little  influence  on  the 
solubility  of  antimony.  The  amount  of  bismuth  dissolved  is 
about  1.5  grams  per  litre,  and  none  separates  on  cooling. 
From  other  results  obtained,  the  solubility  of  bismuth  is 
somewhat  greater  in  the  cold  solution,  on  account  of  change 
to  another  series  of  so  far  uninvestigated  salts  in  which 
bismuth  has  greater  basicity. 

For  the  sake  of  example,  let  us  assume  that  one  ton  of 
lead  contains  7.4  Ibs.  silver,  2  Ibs.  bismuth,  4  Ibs.  arsenic, 
10  Ibs.  copper,  20  Ibs.  antimony,  while  5  Ibs.  of  lead  will  also 
remain  in  the  slime. 

Ferric  iron  required  is  readily  calculated  by  the  use  of 
factors,  as  given  in  Table  37. 

TABLE  37. 

For  silver  None. 

"    bismuth      2X    .81=      1.62  Ibs. 
' '    arsenic         1  X  2 . 24  =     8 . 96    ' ' 
"    copper       10X1.76=    17.60    " 
"    antimony  20X1.40=  28.00    " 
"    lead  5X    .54=     2.7      " 

Total.  .  .58.88 


CHEMISTRY  OF  SLIME  TREATMENT. 


97 


This  amount  of  ferric  iron  is  contained  in  about  23  cubic 
feet  of  electrolyzed  solution.  Allowance  must  be  made  for 
the  fact  that  the  action  is  not  entirely  complete.  Usually 
not  all  the  copper  and  arsenic  present  dissolve,  but  only 
about  90%.  Taking  account  of  the  solubility  of  bismuth  and 
antimony,  and  of  copper  already  in  solution  to  the  amount  of 
10  grams  per  litre,  and  used  to  boil  out  traces  of  silver  and 
reduce  excess  of  Fe",  the  distribution  of  the  products  is 
about  as  follows: 

TABLE  38. 


In  Solution. 

In  Sediment  After  Cooling. 

In  Residue. 

All  Iron. 
2.35  Ibs.  antimony 
18      '  '     bismuth 

Lbs. 

.  85  antimony 

All  Lead. 
16.8  Ibs.  antimony 
2    '  '     bismuth 

26  0      "     copper 

1        '  '     copper 

8.1      '  '     arsenic 

9    '  '     arsenic. 

The  solution  also  contains  fluosilicic  acid  present  in  the 
slime  on  account  of  not  entirely  complete  washing.  This 
is  a  troublesome  compound  to  have  present,  as  will  be  ex- 
plained elsewhere,  on  page  109. 

The  sediment  can  be  put  in  a  charge  of  fresh  slime.  The 
residue  has  then  to  be  washed  rather  free  of  iron  and  copper 
sulphate,  and  is  then  treated  with  a  solution  of  hydrofluoric 
and  sulphuric  acids,  which  may  vary  largely  in  composition, 
about  5%  sulphuric  acid  and  5-10%  hydrofluoric  acid  being 
satisfactory.  The  result  is  the  solution  of  approximately 
95%  of  the  antimony  and  arsenic  still  remaining,  with  a  little 
copper  and  iron.  Silica  also  dissolves.  The  following  analy- 
ses are  of  air-dried  Trail  slime  treated  experimentally.  In 
the  first  column  is  given  the  analysis  of  the  air-dried  slime, 


98 


LEAD  REFINING  BY  ELECTROLYSIS. 


in  the  second  column  the  same  after  treatment  with  ferric 
sulphate,  and  in  the  third  column  the  same  after  treatment 
with  HF  solution: 

TABLE  39. 


14.5% 

Au 34 . 5  ozs. 

Ag.... 15.9% 

Cu 9.5% 

Pb 16.0% 

Sb 25.91% 

As 5.96% 


SiO, 


2.2% 


36  .  44  ozs. 

69.32  ozs. 

16.2% 

31.9% 

•8% 

1.28% 

17.6% 

33.1% 

25.03% 

3.72% 

1-2% 

Nil. 

1.8% 

0.8% 

The  distribution  of  the  products  in  this  case  were  calcu- 
lated from  the  analyses  to  be  about  as  follows: 


TABLE  40. 


In  Copper-iron  Solution. 

In  Fluoride  Solution. 

In  Residue. 

No  silver  * 
No  gold  * 
No  lead  * 
92%  of  the  copper 
8  .  5%  of  the  antimony 
81%  of  the  arsenic 
23%  of  the  silica 

No  silver  * 
No  gold  * 
No  lead  * 
1%  of  the  copper 
84.5%  of  the  antimony 
19%  of  the  arsenic 
59%  of  the  silica 

100%  silver 
100%  gold 
100%  lead 
7%  of  the  copper 
6.75%  of  the  antimony 
No  arsenic 
18%  of  the  silica 

*  Known  from,  tests  of  solutions. 

I 

With  the  slime  which  has  not  been  dried  the  results  are 
somewhat  better  than  the  above,  as  the  inevitable  result  of 
drying  is  the  formation  of  hard  lumps  which  it  is  hard  for 
the  solutions  to  penetrate. 

Usually  silver  dissolves,  as  a  small  excess  of  ferric  sul- 
phate is  always  used,  and  before  nitration  the  solution  and 
suspended  slime  are  agitated  in  presence  of  metallic  copper 
until  the  excess  of  ferric  sulphate  has  been  reduced  and  all 
the  silver  removed  from  the  solution.  At  a  boiling  temper- 


CHEMISTRY  OF  SLIME  TREATMENT.  99 

ature  this  takes  from  2  to  10  hours  according  to  the  copper 
surface  exposed,  and  the  amount  of  ferric  sulphate  in  excess. 
An  exposure  of  about  4  square  feet  of  copper  for  each  cubic 
foot  of  solution  is  sufficient  for  moderately  quick  work. 

Settling  and  nitration  is  found  to  be  much  easier  and 
quicker  after  silver  has  been  removed.  The  solution  settles 
clear  in  a  short  time  and  most  of  it  can  be  drawn  off  without 
filtration.  The  residue  may  be  washed  by  decantation  to 
best  advantage  with  hot  water,  or  filtered  in  a  press  or  on  a 
horizontal  cloth  resting  in  a  shallow  tank  with  a  perforated 
or  grooved  wood  or  lead  bottom.  Centrifugal  machines  are 
also  used  for  this  kind  of  work.  If  the  material  cools  very 
much  during  nitration  it  clogs  up  from  separation  of  anti- 
mony oxide. 

The  extraction  of  silver  requires  a  considerable  excess  of 
ferric  sulphate,  and  even  then  with  most  slime  the  extrac- 
tion of  silver  is  very  incomplete.  If  the  silver  could  be  dis- 
solved and  precipitated  on  copper  in  a  separate  tank,  the 
expense  of  melting  silver  twice  and  parting  would  be  saved. 
A  temperature  of  95-100°  gives  a  much  better  extraction  of 
silver  than  one  of  80°.  This  was  shown  in  an  experiment 
on  slime  containing  79%  Ag;  12.6%  Cu;  4.12%  Sb;  88%  Bi; 
3%  Pb,  from  refining  rich  lead  with  10%  and  15%  silver. 
The  precipitated  silver  was  washed  in  this  case  with  HC1  to 
take  out  traces  of  Sb203  +  Bi203.  A  large  excess  of  ferric 
iron  was  used,  but  it  is  doubtful  if  this  made  any  great  differ- 
ence in  the  result.  The  use  of  a  considerable  bulk  of  solu- 
tion had  more  influence  probably.  Particulars  are  given  in 
Table  41. 


100 


LEAD  REFINING  BY  ELECTROLYSIS. 
TABLE  41. 


No. 

Weight  of 
Slime. 

Volume 
Solution  . 

Fe"  Used. 

Time. 

Temperature. 

Residue. 

1 
2 

45  gr. 
45  gr. 

2500  cc. 
2500  cc. 

50  gr. 
50  gr. 

31  H. 

3i  H. 

80-85° 
95-99° 

13.5gr. 
6.4  gr. 

No. 

Precipitated  Silver. 

Contains  Before  Melting. 

Silver  Extraction. 

1 
2 

25.7gr. 
33.2gr. 

98.71%Ag 
99.65%Ag 

71.4% 
93.0% 

The  treatment  of  copper  slime  with  ferric  sulphate  is  very 
successful  in  removing  copper  quickly.  With  slime  from 
blister  copper  anodes,  there  is  too  much  sulphur  present  to 
allow  of  the  solution  of  much  if  any  silver.  Several  experi- 
ments have  been  made  on  slime  analyzing  Cu  53.29%;  Ag 
12.90%;  Bi  1.55%;  Sb  3.30%;  As  1.15%;  S  11.96%;  Te 
1.97%;  Se  .26%;  Pb  trace;  gold  and  moisture  not  deter- 
mined. See  Table  42. 

TABLE  42. 


No. 

Slime  Taken. 

Fe'". 

Temperature. 

Volume. 

H2SO4. 

Residue  . 

1 

200  gr. 

161  gr. 

90° 

122  gr. 

2 
3 

100  gr. 
700  gr. 

100  gr. 
750  gr. 

85-92° 
85-90° 

1  200  cc. 
9  500  cc. 

5% 
4.2% 

325gr. 
\SeeTable 

4 

700  gr. 

750  gr. 

85-92° 

10  000  cc. 

4% 

/43. 

The  residue  was  treated  with  caustic-soda  solution  to 
extract  the  sulphur,  antimony,  selenium,  and  tellurium  if 
possible.  Traces  of  tellurium  dissolved  out,  but  no  selenium. 


CHEMISTRY  OF  SLIME  TREATMENT. 
TABLE  43. 


101 


No. 

NaOH. 

Volume. 

Temper- 
ature. 

Residue. 

Fusion  . 

Product. 

Agin 
Button. 

2 

30  gr. 

150  cc. 

Boiling 

19.7gr. 

10  gr.  nitre 

Dore     matte 

7.5  gr.  soda 

and  slag 

12.22gr. 

3 

200  gr. 

2000  cc. 

t  ( 

159.5  gr. 

90  gr.  nitre 

Dore     matte 

4 

200  gr. 

2000  cc. 

(  t 

177  gr. 

100  gr.  soda 
90  gr.  nitre 

and  slag 
Dore     matte 

163  gr. 

100  gr.  soda 

and  slag 

Analysis  of  dore  from  3  and  4,  Ag  86.55%;  Bi  5.37%;  Cu 
5.99%;  Au  1.62%;  Te  .16%;  Se  trace;  Pb  nil;  Sb  trace; 
Cu  nil;  As  nil. 

The  residue  from  No.  1  was  melted  direct  to  matte,  with- 
out treatment  with  NaOH.  Matte  weighed  48  grams.  Con- 
tained 12.7%  S;  53.6%  Ag  calculated.  Probably  a  great 
deal  more  caustic  soda  was  used  than  was  entirely  necessary. 
Probably  80  grams  of  caustic  for  700  parts  slime  taken  would 
have  done  just  as  well.  Milk  of  lime  would  act  similarly  to 
caustic  soda  and  be  cheaper. 

In  treating  copper  slime  with  ferric  sulphate,  the  process 
works  quickly  and  completely  at  a  temperature  of  about 
90°;  at  100°  the  liberated  sulphur  sticks  together  and  hinders 
the  reaction.  Only  a  slight  excess  of  ferric  iron  should  be 
used,  and  the  excess  reduced  by  suspending  copper  plates 
in  the  solution  before  removing  it  from  the  insoluble  residue. 

Returning  to  the  consideration  of  lead  slime-treatment, 
the  solution,  after  removal  from  the  slime,  now  containing 
ferrous  sulphate,  cupric  sulphate,  arsenious  acid,  and  sul- 
phuric acid,  beside  smaller  quantities  of  arsenic,  bismuth, 
silica,  and  fluosilicic  acid,  is  to  be  electrolyzed  for  metallic 
copper  and  regeneration  of  ferric  sulphate.  A  separate  treat- 
ment of  the  solution  with  copper  oxide,  metallic  copper  and 


102  LEAD  REFINING  BY  ELECTROLYSIS. 

air,   or  copper  matte,   is  necessary,    unless    the    slime    being 
treated  should  have  been  air-dried,  and  say  two-thirds  oxi- 

* 

dized. 

The  electrolysis  of  the  solution  takes  place  at  about  40°, 
and  on  cooling  to  this  temperature  or  a  little  lower  about 
10  grams  antimony  oxide  per  litre  and  excess  of  arsenious 
acid  above  that  required  to  saturate  the  solution  at  this  tem- 
perature (say  2%  As203)  crystallize  out.  This  cooling  takes 
care  of  the  arsenic  of  the  slime,  the  solution,  after  reaching 
a  concentration  of  about  2%  As20s,  thereafter  depositing  that 
removed  from  the  slime.  The  arsenic  crystallizes  as  bright, 
hard  crystals.  The  solubility  of  As2C>3  in  the  hot  solution 
is  about  one  part  in  ten  parts  solution,  and  at  20°  one  part 
in  100  parts  solution,  having  therefore  a  large  variation  for 
difference  in  temperature.  There  are  two  varieties  of  As203, 
but  we  have  here  to  do,  at  least  in  the  cold,  with  -the  crystal- 
line variety,  of  which  the  solubility  is  ten  parts  in  100  parts 
hot  water  and  1.7  parts  in  100  parts  cold  water  (Comey's 
Dictionary).  The  solubility  in  reduced  iron  solution  is  not 
very  different. 

The  electrolysis  of  solution  containing  iron  and  copper 
for  the  production  of  a  copper  deposit  and  a  solution  of  ferric 
sulphate  was  first  proposed  by  Body.* 

Siemens  and  Halskef  proposed  a  process  in  which  the  fer- 
ric sulphate  was  used  to  attack  metallic  copper  and  copper 
sulphide  and  the  solution  then  brought  back  to  the  electrolytic 
cell  for  the  recovery  of  the  copper  and  the  ferric  sulphate. 
Difficulties  were  met  by  Siemens  and  Halske  in  the  electrolysis,. 

*  U.  S.  A.  Patent  338150.     Jan.  5,  1886. 

t  German  Patent  42243.  Sept.  14,  1886.  English  Patent  14033.  Nov. 
1,  1886. 


CHEMISTRY  OF  SLIME  TREATMENT. 


103 


particularly  the  carbon  anodes  were  corroded  and  the  yield 
of  ferric  sulphate  was  low.  The  corrosion  of  the  carbon 
anodes  was  a  fatal  difficulty.  I  found  that  the  anodes  could 
be  made  to  last  permanently  if  they  were  kept  in  constant 
motion  through  the  solution.* 

The  electrolysis  of  the  reduced  iron  solution  has  been 
made  the  subject  of  a  special  study  to  determine  the  effect 
on  the  current  density  and  voltage  of  variations  in  temper- 
ature and  chemical  composition. 

The  electrodes  used  in  the  test  were  each  of  graphite,  and 
the  anode  was  kept  in  back-and- forth  motion  through  the 
-electrolyte  by  means  of  a  crank.  If  the  anode  stopped  it 


i.o- 


14  21 

Amperes  per  Square  Foot 

FIG  11. — SOLUTION  0. 


polarized  in  a  short  time,  and  oxygen  was  evolved  on  the 
anode  and  little  or  no  ferric  iron  formed.  As  the  anode  reac- 
tion was  the  only  one  with  which  difficulty  was  experienced 
before  the  requirements  of  the  case  were  understood,  the  depo- 
sition of  copper  at  the  cathode  was  disregarded,  and  a  solu- 
tion electrolyzed  containing  ferrous  sulphate,  copper  sul- 


*  U.  S.  A.  Patent  803543.     Nov.  7,  1905. 


104 


LEAD  REFINING  BY  ELECTROLYSIS. 


phate,  and  sulphuric  acid,  and  in  some  cases  also  ferric  sul- 
phate, without  a  diaphragm. 

The  results  indicate  that  the  effect  of  temperature  is  the 
most  important.  The  results  are  plotted  as  Figs.  11  to  17. 
The  ordinates  represent  the  polarization  in  excess  of  the 
electromotive  force  required  to  carry  out  the  oxidation  of 
the  iron. 

Solutions  were  tested  as  follows: 

TABLE  44. 


Solution. 

O 

A 

B 

C 

D 

H2SO4            grams  per  100  cc.  . 

1 

2 

3 

5 

9 

FeSO47H2O      "       "    100    "  

5 

5 

5 

5 

5 

CuSO45H2O      "       "    100    "  

12 

12 

12 

12 

12 

The  amperes  per  square  foot  refers  to  plane  occupied 
by  1  inch  carbon  rods  spaced  1JJ  inch  centre  to  centre. 
For  amperes  per  square  foot  of  carbon  surface,  multiply 
by  1.09. 

Tests  were  also  made  with  the  following  solution: 


TABLE  45. 


Solution. 

O' 

A' 

B' 

C' 

zx 

H;2SO4  grams  per  100  cc 

1 

2 

3 

5 

9 

FeSO47H2O  "  "  100"  
CuSO45H2O  "  "100"  
Fe,(SO4)3  "  "  100" 

5 
4 
10.7 

5 
4 
10.7 

5 
4 
10.7 

5 

4 
10  7 

5 
4 
10  7 

The  results  are  somewhat  different,  probably  on  account 
of  the  failure  of  copper  to  deposit  on  the  cathodes  in  the 
second  series  where  the  reduction  of  ferric  iron  takes  place 


CHEMISTRY  OF  SLIME  TREATMENT. 


105 


14  21 

Amperes  per  Square  Foot 

FIG.  12. — SOLUTION  A. 


1.0 


fa 

'' 


f 


14  21 

'Amperes  per  Square  Foot 

FIG.  13. — SOLUTION  B. 


14  21. 

Amperes  per.  Square  Foot 

FIG.  14. — SOLUTION  C. 


106 
i.o 


LEAD  REFINING  BY  ELECTROLYSIS. 


r  14  21 

Amperes  per  Square  Foot 
FIG.  15. — SOLUTION  D. 


1%         2*        3*  5*  0%  H2So4 

FIG.  16. — EFFECT  OF  SULPHURIC  ACID  AT  25°  C. 


1.0 


^ 


-*-21  a 


nps. 


•14  amps. 


1%         2%        3%  5% 

Per  Cent 
FIG.  17. — EFFECT  OF  SULPHURIC  ACID  AT  50°-55°  C. 


CHEMISTRY  OF  SLIME  TREATMENT. 


107 


instead.  I  regard  these  latter  results  as  showing  the  anode 
polarization  best.  See  Figs.  18,  19,  20,  21. 

The  necessity  of  moving  the  anodes  exists  under  the  con- 
ditions studied  in  these  experiments  if  polarization  is  to  be 
prevented.  However,  I  found  that  at  a  still  higher  tem- 
perature, near  boiling,  it  is  no  longer  necessary  to  move  the 
anodes.* 

Of  course,  at  lower  temperatures,  the  anode  rods  might 
be  left  stationary  if  the  relative  motion  between  anode  sur- 
face and  electrolyte  was  maintained  by  rapid  circulation, 


14  21 

Amperes  per  Square  Foot 

FIG.  18.  —  SOLUTION  A'. 


28 


but  it  would  have  to  be  so  rapid  as  to  be  impracticable  on  a 
large   scale,   in   a  tank   of   any   ordinary   construction. 

It  was  found  in  some  experiments  on  slime  treatment 
that  the  anodes  polarized  in  spite  of  everything  that  could 
be  done,  including  increasing  temperature  and  the  velocity 
of  the  anodes.  The  anodes  on  taking  out  were  slimy  to  the 
touch;  after  brushing  off  they  would  run  some  hours  suc- 
cessfully and  would  then  polarize  again. 

*  U.  S.  Patent  applied  for. 


108 

1.0 


LEAD  REFINING  BY  ELECTROLYSIS. 


14  21 

Amperes  per  Square  Foot 

FIG.  19. — SOLUTION  B'. 


14  21  28 

Amperes  per  Square  Foot 

FIG.  20.— SOLUTION  C'. 


7  14  21 

Amperes  per  Square  Foot 
FIG.  21. — SOLUTION  D'. 


CHEMISTRY  OF  SLIME  TREATMENT.  109 

As  the  process  has  been  worked  continuously  on  other  fer- 
rous sulphate  solutions  than  those  from  treating  lead  slime,  an 
investigation  was  made  to  ascertain  the  cause  of  the  trouble. 

Pure  solution  of  iron  and  copper  sulphates  and  sulphuric 
acid  were  treated  with  various  materials  and  electrolyzed. 
The  presence  of  gelatine,  tin,  arsenic,  antimony,  bismuth, 
and  soluble  silica  had  no  prejudicial  effect. 

Fluosilicic  acid,  on  the  other  hand,  caused  polarization 
readily,  and  if  the  quantity  added  was  at  all  large,  a  thick 
silica  deposit  would  form  on  the  anode.  The  coating  from 
anodes  used  in  working  up  solution  from  slime  treating  was 
tested  and  found  to  consist  largely  of  silica. 

For  large  scale  work,  the  remaining  serious  question  is 
one  of  diaphragms.  For  this  process  diaphragms  of  wood, 
about  I"  thick  with  I"  to  f  "  holes  bored  through  as  closely 
as  possible,  with  holes  filled  with  wet  asbestos;  asbestos 
boards  \"  thick,  hardened  by  absorption  of  the  right  amount 
of  sulphur;  and  pairs  of  perforated  lead  sheets  with  several 
thicknesses  of  asbestos  between  have  been  tried,  and  all 
have  given  success. 

The  disadvantage  of  the  wood  diaphragms  has  been  that 
the  plugs,  if  not  put  in  tightly  enough,  drop  out,  or  if  the 
copper  deposit  gets  spongy,  which  has  happened  when  unre- 
duced solution  was  fed  in,  the  copper  may  grow  into  the  plugs 
and  on  drawing  the  cathodes,  a  plug  or  plugs  come  too. 

The  disadvantage  of  the  asbestos  board  hardened  with 
sulphur  is  that  it  expands  slightly  when  wet  and  warps. 
This  difficulty,  I  believe,  can  be  cured  by  soaking  the  boards 
a  week  or  two  before  putting  them  in  a  tank.  The  resistance 
is  quite  a  little  higher,  requiring  perhaps  .4  to  .5  volt  more 
to  operate  a  tank  than  one  with  lead  and  asbestos  diaphragms. 


110  LEAD  REFINING   BY  ELECTYO LYSIS. 

The  disadvantage  of  the  lead  and  asbestos  boards  dia- 
phragm is  the  cost  of  the  lead,  and  the  necessity  of  operating 
the  tank  at  a  uniform  temperature  to  prevent  wrinkling  of 
the  lead. 

These  advantages  would  have  to  be  weighed  against  each 
other  before  making  a  choice,  but  good  success  will  result  in 
the  use  of  any. 

To  prepare  hardened  asbestos  diaphragms  of  the  above 
construction,  asbestos  "  mill  boards/'  which  come  in  about 
40-inch  squares,  should  be  placed  flat  on  a  floor,  powdered 
sulphur  sprinkled  on  evenly,  and  placed  in  an  oven  hot 
enough  to  melt  sulphur,  for  an  hour  or  more.  The  sulphur 
melts  and  is  absorbed  by  the  asbestos.  The  same  operation 
is  repeated  on  the  other  side  of  the  boards.  The  hot  board 
is  cooled  on  a  flat  floor,  giving  a  sheet  of  considerable  stiff- 
ness and  strength,  that  does  not  soften  in  water  or  acid  solu- 
tion, even  after  a  long  time.  Care  must  be  used  not  to  fully 
saturate  the  board  with  asbestos,  which  would  make  it  an 
insulator.  The  effect  of  the  sulphur  is  to  cement  the  asbestos 
fibres  together.  Two  to  three  pounds  of  sulphur  is  found  to 
be  about  right  for  10 -square  feet  of  \"  board. 

For  details  of  construction  of  lead-lined  copper-iron  sul- 
phate electrolytic  tanks,  see  Chapter  VII.  The  cat  holy  te 
only  comes  in  contact  with  the  lead  lining  in  these  construc- 
tions. *••  The  solution  of  ferrous  and  cupric  sulphates  and  sul- 
phuric acid,  containing  approximately  30  grams  copper,  40-50 
grams  ferrous  iron  and  20-60  grams  H2S04  per  litre,  is  fed 
irr  a  continuous  stream  into  the  cathode  compartment,  which 
stands  in  composition  at  about  10  grams  copper,  40-50  grams 
ferrous  iron  and  20-60  grams  H2S04.  An  overflow  about  two 
inches  below  the  top  of  the  tank  is  provided  for  the  anolyte, 


CHEMISTRY  OF  SLIME  TREATMENT.  Ill 

averaging  S-lO  grams  ferrous  iron,  30-40  grams  ferric  iron, 
20-60  grams  H2S04  per  litre.  The  effect  of  feeding  solution  to 
the  catholyte  is  to  maintain  the  catholyte  at  a  slightly  higher 
level  than  the  anolyte,  so  that  the  solution  percolates  through 
the  diaphragm  continuously,  preventing  back-flow  of  anolyte 
to  the  catholyte  compartments.  The  anolyte  is  also  found 
to  be  slightly  heavier  than  the  catholyte,  for  instance,  1.19 
and  1.16  specific  gravity  respectively. 

The  tanks  are  built  on  the  principle  of  placing  a  series 
of  anolyte  boxes,  with  catholyte  spaces  between  each,  and 
on  the  sides  and  bottom  too.  Circulation  of  the  catholyte 
through  the  tank  can  be  easily  arranged  and  circulation  of 
the  anolyte  is  provided  by  siphons  connecting  each  anolyte 
compartment  to  a  trough  on  each  side  of  the  tank.  This 
trough  need  not  necessarily  be  placed  outside  of  the  tank, 
but  can  be  fitted  inside.  Circulation  is  maintained  by  com- 
pressed air.  The  trough  on  one  side  serves  as  a  feed  to  all 
the  anolyte  compartments,  and  the  discharge  takes  place 
to  the  trough  on  the  other  side.  The  siphons  are  provided 
with  an  arrangement  by  which  the  air  can  be  sucked  out. 

Serious  attempts  were  made  to  electrolyze  the  solution 
in  cells  without  a  diaphragm,  depending  on  the  formation 
of  a  heavier  ferric  sulphate  solution  at  the  anode,  which 
should  settle  "to  the  bottom  of  the  cell.  This  principle  can 
be  applied  successfully  in  electrolyzing  chloride  solutions, 
but  it  will  be  difficult  or  impossible,  I  think,  to  use  it  in 
iron  sulphate  electrolysis. 

The  slime  after  treatment  with  ferric  sulphate  should  be 
washed  fairly  well,  as  any  iron  and  copper  salts  not  washed 
out  will  accumulate  in  the  fluoride  solution  used  for  anti- 
mony extraction.  Copper  can,  however,  be  removed  by 


112 


LEAD  REFINING  BY  ELECTROLYSIS. 


antimony  as  described  in  Chapter  III,  and  the  only  effect 
of  iron  is  to  slightly  diminish  the  current  efficiency  of  the 
antimony  deposition,  but  not  very  seriously. 

The  fluoride  solution  dissolves  most  of  the  antimony  pres- 
ent, as  well  as  the  arsenic  still  remaining,  and  traces  of  bis- 
muth and  silica. 

The  solubility  of  bismuth  in  the  fluoride  solution,  provided 
excess  of  acid  is  used,  is  very  slight.  Considerable  quantities 
dissolve,  if  no  excess  of  HF  is  used,  and  HF  added  to  the  solu- 
tion in  that  case  causes  a  precipitation  of  bismuth,  probably 
as  BiF3.  The  amount  of  bismuth  dissolved  with  excess  of 
HF  present  has  been  variously  determined  from  .008  to  .010 
grams  per  100  cc. 

The  bismuth  dissolved  deposits  out  with  the  antimony, 
and  on  one  occasion,  treating  high  bismuth  slime,  the  per- 
centage of  bismuth  in  the  antimony  was  0.67.  This  is  the 
highest  percentage  yet  observed,  and  is  equivalent  to  .035 
grams  Bi  dissolved  per  100  cc. 

The  extraction  of  antimony  with  HF  from  the  slime  after 
treatment  with  ferric  sulphate  averages  95%,  a  tempera- 
ture of  30-40°  C.  and  excess  of  HF  being  desirable.  The 
effect  of  H2SO4,  which  is  also  present  in  the  solutions,  seems 
to  be  insignificant.  See  Table  46. 


TABLE  46. 


Weight  of 
Slime. 

HF 

Excess. 

Weight  of 
Residue. 

Tempera 
ture. 

Slime. 

Residue. 

Extracted, 
Sb. 

200  gr. 

17% 

107 

20°  C. 

30.8%  Sb 

5.59%  Sb 

90.3% 

100  gr. 

200% 

50.2 

20°  C. 

30.8%  Sb 

3.99%  Sb 

93.5% 

50  gr. 
50  gr. 

200% 
200% 

26. 
26.2 

35-40°  C. 
30-40°  C. 

30.8%  Sb|2.38%  Sb 
30.8%  Sbi3.63%  Sb 

96.1% 
93.8% 

CHEMISTRY  OF  SLIME  TREATMENT.  113 

No  silver  dissolves  in  the  fluoride  solution,  probably  on 
account  of  the  presence  of  other  unoxidized  metals  capable 
of  precipitating  silver.  The  antimony  fluoride  solution  is 
treated  with  K2S04  or  Na2S04  for  removal  of  SiF6  and  elec- 
trolyzed  for  metallic  antimony  and  regeneration  of  HF.  Par- 
ticulars will  be  found  on  page  144. 

The  treatment  of  the  insoluble  residue  has  only  been  carried 
out  by  fusion  to  dore  bullion.  This  fusion  can  be  accom- 
plished with  various  fluxes,  but  soda  has  been  chiefly  used 
as  a  flux  in  the  experiments,  which  was  a  mistake.  Fusion 
with  silica  is  better,  and  gives  a  clean  dore  bullion.  The 
sulphur  and  carbon  in  the  slime  are  oxidized  by  the  oxygen 
liberated  when  lead  sulphate  is  decomposed  by  silica.  The 
lead  silicate  slag  can  be  smelted  for  the  lead  and  traces  of 
silver  it  contains. 

The  fusion  may  be  conducted  in  reverberatories,  or  cru- 
cibles, though  the  latter  is  best,  for  no  furnace  refining  is 
required. 

A  sample  of  dore  bullion  produced  from  Trail  slime,  con- 
taining in  the  first  place  approximately  30%  Sb;  29%  Ag; 
6%  As;  10%  Pb;  and  7%  Cu,  which  had  been  treated  with 
ferric  sulphate  and  hydrofluoric  acid,  and  then  melted  with 
soda,  contained  Ag  78.94%;  Pb  17.56%;  Au  2.08%;  Cu  .81%; 
Sb  .47%;  no  As.  Other  melts  with  silica  have  produced  far 
cleaner  dore,  containing,  beside  gold  and  silver,  only  traces 
of  copper  and  lead. 

The  metallurgical  recovery  of  the  ferric  sulphate  process 
is  excellent.  95  Ibs.  of  Trail  slime  contained  by  corrected 
fire  assay  445.83  ozs.  silver  and  3.7  ozs.  gold.  This  was 
treated  experimentally  in  some  8  or  10  batches,  using  the 
solutions  over  and  over  again,  and  notwithstanding  some 


114  LEAD  REFINING  BY  ELECTROLYSIS. 

accidents,  the  silver  recovery  was  443.85  ozs.  and  gold  3.65  ozs. 
The  limit  of  accuracy  of  the  gold  assays  was  .1  oz.,  so  prob- 
ably the  actual  recovery  of  gold  was  as  great  in  proportion, 
or  greater  than  that  of  silver.  The  silver  loss  was  less  than 
J%,  and  on  the  basis  of  uncorrected  assay  there  would  have 
been  a  gain  of  from  f%  to  1%. 

Copper  scale  for  adding  copper  and  oxygen  to  the  iron 
sulphate  solution  is  not  to  be  recommended,  as  it  contains 
too  much  metallic  copper  and  cuprous  oxide.  Copper  sul- 
phate is  rather  too  expensive,  though  it  may  only  represent 
roasted  copper  matte  plus  sulphuric  acid.  The  use  of  granu- 
lated copper  in  a  tower,  through  which  the  acid  slowly  passes 
in  the  presence  of  air  is  permissible  but  slow,  requiring  a  large 
stock  of  metallic  copper.  The  copper  is  relatively  more 
expensive  than  the  same  material  in  the  form  of  roasted 
matte. 

Methods  of  treating  roasted  copper  matte  for  extraction 
of  copper  are  well-known,  the  best  description  being  that 
given  by  Hofmann.*  The  material  treated  at  Argentine, 
Kansas,  contained  40%  Cu  and  12-14%  Pb.  It  was  ground 
to  50  mesh  in  a  ball-mill,  and  roasted  in  Pearce  turret  fur- 
naces. The  roasted  material  was  again  ground  to  50-mesh 
in  a  ball-mill  and  treated  in  tanks  with  stirring-gear,  with 
water  and  sulphuric  acid.  The  mixture  was  filtered  in  a 
wood  filter-press  and  the  solution  treated  with  a  further  small 
quantity  of  matte  while  air  was  blown  through  to  purify 
the  solution  from  iron,  arsenic,  and  antimony. 

The  air  blowing  can  be  omitted  in  slime  treating,  as  the 
presence  of  ferrous  iron  in  the  solution  is  not  an  objection. 

*  Mineral  Industry,  Vol.  10,  page  231. 


CHEMISTRY  OF  SLIME  TREATMENT.  115 

One  treatment  of  the  solution  with  a  slight  excess  of  matte 
would  be  sufficient.  The  arsenic,  antimony,  and  fluosilicic 
acid  being  removed  by  neutralization,  the  result  is  a  neutral 
solution  of  cupric  and  ferrous  sulphates.  This  requires 
acidification  to  say  2%  H2S04,  before  electrolysis,  to  save 
power. 

The  insoluble  residue  would  contain  considerable  anti- 
mony, and  if  the  solution  contained  traces  of  bismuth,  con- 
siderable of  that  beside  a  good  deal  of  lead  and  some  copper. 
By  smelting  the  leached  matte  in  a  lead-furnace  the  anti- 
mony and  bismuth  values  would  be  recovered  in  the  lead  pro- 
duced. On  the  supposition  that  59  Ibs.  ferric  iron  are  re- 
quired to  treat  the  slime  from  one  ton  of  lead,  which  is  a  fair 
average,  and  that  the  matte  contains  40%  copper  and  14% 
lead,  the  lead  bullion  produced  by  smelting  the  leached  matte 
alone  would  contain  as  much  as  20%  antimony,  and  bismuth 
up  to  16%,  if  bismuth  is  present  in  the  slime  in  large  quan- 
tity. This  bullion  could  be  refined  for  the  lead  content 
without  difficulty  in  the  usual  way,  and  the  slime  treated 
with  dilute  nitric  acid  to  make  bismuth  subnitrate  and  anti- 
mony oxide.  It  would  probably  be  more  advantageous  to 
dilute  the  matte  with  lead  ore  before  smelting  to  produce  a 
purer  bullion  with  less  loss  of  antimony  and  bismuth  in  the 
furnace. 

If  the  lead  bullion  only  contained  a  little  bismuth,  as  is 
usually  the  case,  say  J  to  1  Ib.  per  ton  lead,  the  bismuth 
would  be  practically  all  recovered  from  the  leached  matte, 
in  the  resulting  lead  bullion. 

Perfluoride  processes. — Antimony  pentafluoride,  and  also 
ferric  sulphate  with  the  addition  of  HF  amounting  to  the 
use  of  ferric  fluoride,  have  been  tried.  The  ferric  sulphate 


116  LEAD  REFINING  BY  ELECTROLYSIS. 

and  HF  process  possesses  the  advantage  over  the  ferric  sul- 
phate process,  that  the  antimony  goes  into  solution  with  the 
copper  and  arsenic.  At  the  time  the  experiments  were  made, 
I  was  trying  to  dissolve  silver  with  the  copper,  arsenic,  etc. 
Silver  is  not  dissolved  nearly  as  well  in  presence  of  HF  by 
ferric  sulphate  as  without  HF.  The  experiments  were  given 
up  on  account  of  the  inability  of  dissolving  silver,  but  if  this 
was  not  required,  and  it  was  possible  to  separate  the  arsenic 
by  crystallization  as  As203,  and  a  diaphragm  cell,  unattack- 
able  by  HF,  could  be  provided  for  electrolyzing  the  solutions, 
the  process  would  be  workable  as  well  as  simple  and  quick. 
The  operations  ought  to  be  treatment  of  slime  with  solution 
of  copper,  antimony,  and  arsenic.  Insoluble  residue  con- 
sists of  lead  sulphate,  silver,  gold,  and  bismuth  fluoride.  In 
solution,  ferrous  sulphate,  cupric  sulphate,  antimony  trifluoride 
and  arsenious  acid,  .01-.02%  bismuth,  and  stannic  fluoride, 
in  case  slime  contains  tin. 

The  solution  w^ould  then  be  electrolyzed  with  antimony 
anodes  and  copper  cathodes,  with  a  current  density  of  3-5 
amperes  per  square  foot  until  nearly  all  copper  was  deposited 
out.  Then  a  short  electrolysis  with  antimony  anodes  and 
copper  cathodes  in  a  separate  cell  would  remove  the  remain- 
ing copper  with  some  antimony.  The  solution  would  then 
be  electrolyzed  for  the  metallic  antimony  and  the  regeneration 
of  the  ferric  salt,  and  cooled  at  some  stage  of  the  process  to 
crystallize  out  As203  if  possible. 

The  slime  treated  contained  Ag  29.2%;  Cu  7.1%;  Pb 
10.2%;  Sb  30.5%;  As  6.10%;  0  6%;  H20  not  deter- 
mined. 

Some  of  the  results  are  given  in  Table  47. 


CHEMISTRY  OF  SLIME  TREATMENT. 
TABLE  47. 


117 


Slime. 

HF. 

H2S04. 

Fe"'. 

Tempera- 
ture. 

Volume. 

Dissolved. 

Fe'" 
Excess. 

100  gr. 
50  gr. 

30  gr. 
15  gr. 

200  gr. 
85  gr. 

130  gr. 
30  gr. 

Hot 

4000cc. 
700  cc. 

10.5 
None 

75 

The  filtrate  from  the  second  treatment  was  boiled  up  with 
fresh  slime  to  throw  out  copper  and  arsenic,  and  electrolyzed 
with  lead  cathode,  C.D.  9-18  amps,  per  square  foot,  and  lead 
anode  C.D.  54-108  amps,  per  square  foot.  The  antimony 
deposited  contained  1.62%  Cu  and  5.85%  Pb  (from  cathode). 

The  process  was  varied  by  treating  unoxidized  slime,  with 
ferric  fluoride  and  sulphuric  acid,  in  quantity  sufficient  to 
extract  antimony,  and  then  with  ferric  sulphate  alone  to 
extract  copper. 

The  slime  had  the  same  analysis  as  the  above,  but  was 
reduced  by  treatment  with  lead  and  fluosilicic  acid  to  get  it 
back  to  its  original  metallic  condition  as  nearly  as  possible. 
The  first  solution  contained  in  3240  cc.  76  grams  Fe"', 
125  gr.  HF,  100  gr.  H2S04.  Solution  after  the  reaction 
contained  Cu  4.68  grs.;  Sb  47.35  grs.;  As  8.02  grs.  On 
standing  in  a  lead  pan  all  the  copper  deposited  out,  as  well 
as  a  small  amount  of  antimony  on  the  lead. 

The  second  solution  applied  to  the  slime  contained  in 
2800  cc.  110  grs.  Fe'"  and  150  gr.  H2S04.  After  reaction, 
the  solution  contained  47.25  grams  of  silver,  precipitated 
out  by  metallic  copper,  while  41  grams  copper  dissolved.  The 
solution  then  contained  Ag,  none;  Cu,  50.9  gr.;  Sb,  2.14  gr.; 
As,  3.12  gr.  The  residue  contained  PbS04,  63.5%;  Pb,  2.42%; 
Cu,  none;  Sb,  6.24%;  As,  .5%. 

The  results  are  given  in  Table  48. 


118 


LEAD  REFINING  BY   ELECTROLYSIS. 


TABLE  48. 


In  Slime. 

In  Fluoride 
Solution. 

In  Sulphate 
Solution. 

In  Residue. 

Silver 

58  4  grs. 

47  25  °T 

Copper.  . 

14  2  grs. 

4   68 

10  30  gr 

None 

Arsenic  

12  2  grs. 

8  02 

3  25  gr. 

49  gr. 

Antimony  
Lead 

61  .  0  grs. 
20  4  ers. 

47.35 

2.23gr. 

6.17gr. 
45  gr 

The  electrolysis  was  intended  to  be  carried  out  as  fol- 
lows: The  fluoride  solution  was  to  be  electrdlyzed  for  ferric 
fluoride  and  antimony,  and  the  sulphate  solution  for  ferric 
sulphate  and  copper. 

Antimony  pentafluoride.  —  This  process  is  intended  to  dis- 
solve everything  from  the  slime  except  gold,  lead,  and  bis- 
muth, the  last  two  of  which  are  insoluble.  Antimony  penta- 
fluoride was  thought  to  be  a  stronger  oxidizer  than  ferric 
fluoride. 

I  electrolyzed  antimony  trifluoride  solution  containing 
about  14%  Sb  as  SbF3,  freed  from  H2SiF6  by  adding  KF,  to 
precipitate  K2SiF6,  with  a  graphite  anode  and  lead  cathode, 
separated  by  cotton  cloth.  The  e.m.f.  required  to  carry  out 
the  reaction, 


is  about  1.45.  The  polarization  was  about  .2  volt.  The 
current  density  in  my  experiment  varied  from  21  to  40  am- 
peres per  square  foot  on  cathodes,  and  a  little  less  on  anodes, 
with  an  e.m.f.  with  the  latter  current  density  of  2.35  volts. 
The  process  is  not  a  success  because  frequently  it  is  difficult 
to  reduce  the  SbF5  formed,  and  its  action  on  slime  is  far  too 
slow. 


CHEMISTRY  OF  SLIME  TREATMENT.  119 

Ferric  salts  of  strong  monobasic  acids  as  oxidizers. — Fer- 
ric acetate  was  tried  and  found  to  be  valueless.  On  the 
other  hand,  with  strong  acids  (see  page  19),  especially  methyl 
sulphuric  acid  (for  the  preparation  of  which  see  Chapter  IV), 
dissolves  from  the  slime  at  one  treatment,  bismuth,  copper, 
arsenic,  and  lead,  leaving  silver,  gold,  and  antimony  trioxide. 
HF  precipitates  insoluble  bismuth  fluoride  from  the  solution, 
copper  is  precipitable  by  lead,  and  the  solution  of  ferrous 
and  lead  methyl  sulphates  may  be  electrolyzied  for  ferric  salt 
and  lead.  In  distinction  to  ferrous  sulphate  (polybasic  acid), 
ferrous  methyl  sulphate  is  easily  oxidized  with  a  carbon 
anode  at  the  ordinary  temperature,  even  though  the  anode 
is  not  moving.  The  difference  is  probably  due  to  difference 
of  valency. 

The  reaction  Fe  (S04CH3)2  +  S04CH3'==Fe(S04CH3)3  is  a 
simpler  reaction  than 

2FeS04  +  2HSO'4  =  Fe2  (S04)3  +  H20. 

In  the  first  case  the  anion  reacts  with  a  molecule  present  in 
large  quantity,  while  in  the  second  case  the  reaction  requires 
the  molecular  connection  or  contact  of  four  different  parts, 
which  can  readily  be  conceived  to  occur  less  often. 

Use  of  lead  peroxide  as  oxidizing  agent  for  slime. — If  lead 
fluosilicate  solution  is  electrolyzed  with  a  carbon  anode  and 
a  lead  cathode  a  solid  smooth  coating  of  Pb02  is  deposited 
on  the  anode,  and  if  the  solution  contains  gelatine  a  smooth 
deposit  of  lead  is  deposited  on  the  cathode.  The  lead  per- 
oxide in  its  massive  form  is  quite  inactive,  but  if  ground  fine 
and  mixed  with  raw  slime  in  the  presence  of  fluosilicic  acid 
the  metals  of  the  slime  will  be  oxidized  into  solution. 


120  LEAD  REFINING  BY  ELECTROLYSIS. 

Lead  peroxide  was  mixed  with  slime  and  lead  fluosilicate — 
fluosilicic  acid  electrolyte  for  the  purpose  of  extracting  lead, 
copper  and  silver  and  leaving  a  residue  of  antimony  trioxide 
and  gold.  The  results  were  not  satisfactory  either  in  point 
of  time  required  or  in  extraction  of  metals. 

Later  experiments  showed  the  possibility  of  having  suffi- 
cient HF  present  to  take  all  the  antimony  into  solution 
along  with  the  other  metals.  A  solution  of  lead  fluosilicate 
containing,  for  example,  5-6%  lead  and  15%  SiFe,  permits 
of  the  addition  to  it  in  the  cold  of  about  5%  anhydrous  HF 
without  causing  a  precipitation  of  lead,  and  at  a  higher  tem- 
perature considerably  more  may  be  added.  The  explana- 
tion of  this  is  that  fluosilicic  acid  is  a  considerably  stronger 
acid  than  hydrofluoric  acid  and  is  capable  of  decomposing 
insoluble  lead  fluoride  until  the  percentage  of  hydrofluoric 
acid  becomes  great  enough  to  precipitate  lead  fluoride  and 
a  condition  of  equilibrium  is  reached.  On  the  other  hand 
a  solution  of  antimony  trifluoride  may  be  added  in  any  quan- 
tity to  the  lead  fluosilicate  solution,  without  causing  precipi- 
tation of  lead  fluoride,  consequently  it  is  feasible  to  take  the 
antimony  into  solution  simultaneously  with  lead,  by  having 
a  certain  amount  of  hyrdofluoric  acid  present.  Furthermore, 
the  recovery  of  antimony  from  a  mixed  solution  of  antimony 
fluoride  and  lead  fluosilicate  can  be  nicely  carried  out  by 
electrolysis  with  a  lead  anode  and  a  carbon  cathode.  Anti- 
mony deposits  on  the  cathode  and  lead  fluosilicate  dissolves 
on  the  anode  until  the  percentage  of  hydrofluoric  acid  in  the 
solution  becomes  quite  high,  and  thereafter  lead  precipitates 
as  PF2  in  the  neighborhood  of  the  anode.  On  these  prin- 
ciples I  thought  a  good  slime  process  could  be  based,  but  the 
experiments  have  not  been  entirely  successful  so  far,  presum- 


CHEMISTRY  OF  SLIME  TREATMENT.  121 

ably  on  account  of  the  formation  of  antimony  pentafluoride, 
from  the  reaction  of  lead  peroxide  and  antimony  fluoride. 
At  any  rate  the  antimony  goes  into  solution  from  the  slime 
in  an  irreducible  form. 

Thirty-three  gr.  air-oxidized  Trail  slime  containing  about 
15.8%  Ag;  8.2%  Cu;  16.0%  Pb;  26.0%  Sb;  5.96%  As,  was 
treated  with  150  cc.  H2SiF6  and  17  cc.  of  50%  HF,  and  50  cc. 
of  water,  and  25  gr.  finely-ground  electrolytic  PbC>2  added. 
The  solution  warmed  up  quite  a  little  when  Pb02  was  added , 
showing  a  rapid  reaction.  About  half  the  silver  went  into 
solution  with  practically  all  of  the  other  metals,  except  some 
arsenic.  Had  the  slime  not  been  air-oxidized  much  more 
PbC>2  would  have  been  required. 

Silver  was  removed  by  precipitation  with  copper,  and 
the  solution  electrolyzed  with  a  carbon  anode  and  copper 
cathode,  for  recovery  of  PbC>2,  and  metal.  Until  most  of 
the  copper  had  been  removed,  a  good  copper  deposit  was 
obtained.  Then  the  cathode  darkened  and  eventually  the 
deposit  evidently  consisted  of  lead.  It  contained  no  anti- 
mony, showing  the  presence  of  an  antimony  compound  widely 
differing  from  the  ordinary  variety. 

In  another  experiment  unoxidized  specially  prepared 
slime,  containing  on  dry  sample  Ag  4.5%;  Bi  1.1%;  Cu  17.4%; 
Sb  38.0%;  As  12.0%;  Pb  11.0%,  was  treated  with  lead 
electrolyte  containing  about  4%  Pb  and  20-25%  SiF.  The 
solution  had  been  prepared  by  the  electrolysis  of  a  solution 
high  in  lead  and  containing  some  HF,  though  not  enough 
to  precipitate  lead  at  any  time.  This  amount  of  HF  was 
sufficient  for  the  experiment,  so  none  was  added.  On  adding 
the  finely-ground  Pb02  necessary  for  the  reactions  given 
below  the  temperature  rose  rapidly. 


122  LEAD  REFINING  BY  ELECTROLYSIS. 


Cu+  PbO2+2HSiF6  =  CuSiF6+PbSiF6 

Pb+  PbO2+2H^iFfi  =2PbSiF6+2H2O; 

2Sb  +  3PbO2  +  6HF  +  SH^SiFg  =  2SbF3  +  3PbSiF6  +  6H2O  ; 

2As  +  3PbO2  +  SH^iFe  =  ASA  +  3PbSiF6  +  3H2O  ; 

2Ag  +   PbO2+2H2SiF6  =Ag2SiF6  +  PbSiF6+2H2O; 

2Bi  +  3PbO2+  GHF+SH^iFe  =  2BiF3  +  3PbSiF0  +  3H2O. 


The  actual  increase  of  temperature  was  15°,  while  the 
energy  of  the  reaction  was  about  equivalent  to  a  change  of 
temperature,  allowing  something  for  the  box,  of  about  26°, 
so  the  reactions  actually  taking  place  only  amounted  to 
57.5%  of  the  total  energy  expected.  At  the  time  this  was 
thought  to  be  on  account  of  not  entirely  completed  reac- 
tion, which  is  no  doubt  the  case  to  a  considerable  extent,  but 
the  formation  of  an  antimony  or  arsenic  compound  of  higher 
valence  is  also  probable.  The  residue  consisted  of  30%  by 
weight  of  the  orginal  dry  weight. 

By  heating  the  residue  to  a  high  temperature  with  the 
solution  further  reactions  took  place,  with  the  solution  of 
some  of  the  slime,  and  reduction  of  the  solution. 

The  advantages  of  the  process  would  be  important,  men- 
tioning: 

(1)  The  slime  need  not  be  washed  or  even  removed  from 
the  electrolytic  tanks,  as  the  slime  solution  and  lead  refining 
solutions  are  the  same,  and  the  excess  accumulating  in  the 
slime   plant,   derived   from   the   electrolyte   contained   in   the 
slime  treated,  would  be  returned,  after  proper  purification. 

(2)  The  metals  are  directly  recovered   by  electrolysis  in 
a  good  state  of  purity. 

(3)  The   electrolytic   tanks   are   of  the   simplest  kind,   no 
diaphragms  being  necessary. 

The  chief  disadvantages  would  be  the  necessity  of  col- 
lecting a  gpod  deal  of  Pb02  and  grinding  it,  and  the  necessity 


CHEMISTRY  OF  SLIME  TREATMENT.  123 

shown  to  exist  of  working  the  slime  treatment  at  a  high  tem- 
perature. 

The  electrolytic  deposits  obtained  would  consist  first  of 
copper  and  then  of  an  alloy  of  copper  and  antimony,  then  of 
antimony,  then  of  impure  lead  containing  mostly  arsenic  and 
some  antimony.  The  intermediate  products  may  be  refined 
in  the  same  solution,  using  the  impure  cathode  as  anode  in 
a,  separate  cell  through  which  the  solution  passes  at  the 
appropriate  stage  of  its  progress  through  the  tanks.  For 
instance,  the  antimony  copper  alloy  deposited  intermediately 
between  pure  copper  and  rather  pure  antimony,  would  be 
refined  in  the  solution  which  contains  copper  as  it  first  comes 
to  the  electrolytic  tanks.  In  this  way  the  impure  cathodes 
would  not  accumulate,  but  a  certain  quantity  would  always 
be  on  hand  in  the  course  of  working  up  into  pure  metal.  In 
the  example  given  the  copper  and  antimony  of  the  alloy 
dissolve  at  the  anode,  while  only  copper  deposits  at  the 
cathode  and  the  antimony  accumulates  in  the  solution.  The 
power  consumption  per  ton  of  bullion  of  an  ordinary  quality, 
containing  say  1%  antimony,  J%  each  copper  and  silver, 
and  T3o%  arsenic  would  amount  to  about  45  K.W.  hours, 
which  is  very  moderate.  In  fact  the  power  requirement  is 
less  than  in  any  other  electrolytic  slime  process  discussed 
so  far. 

Alkaline  regeneration  processes. — Alkaline  solutions  con- 
taining sulphides  are  the  only  ones  that  will  dissolve  much 
from  the  slime.  Hypochlorite  solutions  were  tried,  and 
arsenic  was  removed  quite  well,  but  it  had  not  much  action 
on  anything  else.  Unsuccessful  preliminary  trials  were  also 
made  with  hyposulphite  solutions  also  containing  tetrathion- 
ate. 


124  LEAD  REFINING  BY  ELECTROLYSIS. 

Slime  suspended  in  sodium  sulphide  and  air  drawn 
through  gives  up  the  antimony  and  arsenic  readily.*  Air 
oxidation  is  much  more  efficient  with  an  alkaline  solution 
or  a  solution  of  a  monobasic  acid  as  HC1,  than  with  the 
customary  sulphuric  acid.  Since  the  heat  of  combination  of 
sulphur  (liberated  by  oxygen  and  dissolved  in  the  solution) 
with  antimony  and  arsenic  to  form  sulphosalts  is  probably 
greater  than  that  with  copper  and  silver,  it  would  be  expected 
that  a  good  extraction  of  antimony  and  arsenic  could  be 
obtained  without  forming  much  silver  and  copper  sulphides, 
though  the  lead  would  probably  be  converted  to  sulphide. 

The  electrolysis  of  sulphantimonite  solutions  is  described 
by  Borchers.t  The  yield  of  antimony  is  quantitative  on 
amount  present  but  not  on  current  used.  The  anode  reac- 
tions were  the  liberation  of  sulphur  which  combined  to  form 
polysulphides,  and  the  formation  of  sodium  hyposulphite. 
The  polysulphide  would  be  of  immediate  use  as  solvent  for 
antimony  in  a  following  slime  treatment,  but  the  formation 
of  Na2S203  represents  at  least  a  temporary  loss.  The  per- 
centage of  the  current  employed  in  the  most  desirable  reac- 
tion for  our  purpose,  namely, 

(1)  Sb2S3  +  3Na2S  =  2Sb4-3Na2S2   is   calculated    from   Bor- 
cher's   figures   to   be   35.8%    in   both   cases   given,   and   that 
employed  in  the  reaction. 

(2)  4Sb2S3+9H20  +  12Na2S  =  8Sb  +  3Na2S203  +  18NaSH  fig- 
ures 80%  or  over  in  the  first  case,  and  in  the  second    case, 
about  80%.     This  shows  that  some  hydrogen  was  liberated 
on  the  cathodes  in  place  of  antimony,  as  in  fact  must  have 
been  the  case,  to  get  all  the  antimony  out. 

*  Results  at  Trail  show  arsenic  to  be  mostly  insoluble. 

f  Electric  Smelting  and  Refining.     Second  Eng.  Ed.,  page  476. 


CHEMISTRY  OF  SLIME  TREATMENT.  125 

-The  relative  proportion  of  the  most  desirable  reaction 
(1)  and  the  undesirable  reaction  (2)  is  shown  to  be  about 
31%  and  69%  of  the  total. 

What  to  do  with  the  arsenic  accumulating  in  the  solution 
is  another  question  to  be  considered.  The  current  efficiency 
in  depositing  antimony  is  evidently  rather  low,  unless 
diaphragms  are  used.*  A  diaphragm  of  asbestos,  supported 
between  perforated  iron  plates,  would  be  analagous  to  the 
same  construction  using  lead  instead  of  iron,  which  is  entirely 
satisfactory  in  ferric  sulphate  electrolysis. 

The  conversion  of  thiosulphate  back  to  sulphide  could 
be  effected  by  evaporating  to  dryness  and  igniting  with  car- 
bon, removing  oxygen  and  water  from  the  mixture  of  NaSH, 
Na2S2,  NaOH,  and  Na2S203. 

That  no  great  difficulty  would  be  met  in  treating  the 
insoluble  portion  of  the  slime,  even  if  converted  to  sulphide, 
by  fusing  to  matte  and  heating  the  ground  matte  with  concen- 
trated sulphuric  acid,  is  evident  from  the  description  given 
on  page  78. 

Treatment  with  copper  fluosilicate^ — As  copper  stands 
below  arsenic,  antimony,  bismuth,  and  lead  in  the  e.m.f. 
series  for  fluosilicate  solutions,  it  was  thought  that  treat- 
ment of  slime  with  copper  fluosilicate  solution  containing 
some  HF  would  result  in  the  solution  of  the  above  metals 
with  a  precipitation  of  the  corresponding  amount  of  copper, 
while  the  residue  would  be  treated  for  copper  and  silver  by  re- 
fining, and  the  solution  for  arsenic,  antimony,  lead  and  bis- 
muth in  the  same  manner  as  described  on  page  135.  No 


*  About  40%  efficiency  at  Trail. 


126  LEAD  REFINING  BY  ELECTROLYSIS. 

reaction  takes  place,  however.  The  addition  of  HF  does 
not  help  the  result. 

Compression  of  slime  to  an  anode  plate  for  direct  elec- 
trolysis.— In  many  ways  this  seems  the  most  logical  method 
of  all.  We  then  have  merely  a  complicated  electrolytic  refin- 
ing operation  to  conduct.  This  it  is,  however,  possible  to  do. 
The  appropriate  solution  to  begin  with,  is  a  solution  of  cop- 
per fluosilicate,  fluosilicic  and  a  few  percent  of  hydrofluoric 
acid.  At  the  anode  lead,  arsenic,  antimony,  bismuth,  and 
copper  dissolve,  while  copper  deposits  on  the  cathode. 
Fresh  copper  solution  is  continuously  required,  while  a  solu- 
tion containing  lead,  arsenic,  antimony,  and  a  little  bismuth 
and  copper  is  produced.  This  can  be  worked  up  to  the  stage 
of  containing  only  a  little  antimony  and  arsenic  beside  very 
much  lead,  in  the  same  manner  as  described  on  pages  136 
and  137. 

The  remaining  step  is  the  electrolysis  of  the  solution  with 
a  lead  cathode  and  copper  anode  in  an  electrolytic  cell,  with 
a  diaphragm  for  the  production  of  lead  on  the  cathode  and 
copper  fluosilicate  solution  at  the  anode.  This  can  also  be 
done  in  a  gravity  cell  with  a  horizontal  lead  cathode  above 
and  copper  anode  underneath. 

Oxidizing  slime  suspended  in  solution  by  air-blast. — At 
Trail  the  first  method  of  slime  treatment  consisted  in  blow- 
ing air  through  the  slime  suspended  in  H2S04  and  salt  in 
a  lead-lined  tank.  This  extracted  the  antimony  and  arsenic 
in  the  course  of  two  or  three  days,  when  the  antimony  was 
to  be  precipitated  out  by  diluting  with  water.  The  anti- 
mony dissolved,  but  the  process  had  to  be  given  up  because 
no  suitable  apparatus  for  melting  the  insoluble  portion  of 
the  slime  was  available.  The  melting  was  attempted  in  cru- 


CHEMISTRY  OF  SLIME  TREATMENT.  127 

cibles,  which  were  rapidly  corroded  by  the  basic  fluxes  used, 
and  the  capacity  of  the  whole  arrangement  was  too  small. 
Also  the  cost  of  sulphuric  acid  and  salt  was  quite  a  heavy 
item.  Laboratory  tests  had  showed  an  extraction  of  the 
antimony  in  about  three  days,  and  considerable  confidence 
was  unfortunately  placed  in  the  current  statement  in  books 
that  blowing  air  through  slime  suspended  in  sulphuric  acid 
was  an  efficient  means  of  oxidation.  The  long  time  required 
in  the  laboratory  test  was  thought  to  be  due  to  the  small 
scale  of  operation  and  shallowness  of  the  layer  through  which 
the  air  passed.  This  process  is,  however,  available  when 
salt  and  sulphuric  acid  are  cheap  and  enough  tank  capacity 
is  at  hand. 

Air  oxidation  with  sulphuric  acid  is  probably  consider- 
ably slower  yet.  The  presence  of  iron  salts,  which  are  con- 
verted by  air  from  the  ferrous  condition  to  ferric  condition, 
might  be  thought  to  be  an  aid  to  the  process,  but  the  oxida- 
tion of  acid  ferrous  sulphate  solution  for  example,  by  air, 
is  extremely  slow.  I  thought  at  one  time  that  if  ferric  sul- 
phate could  be  made  in  this  way  and  then  used  to  attack 
slime  it  could  be  used  over  and  over  again,  crystallizing  out 
copper  and  arsenic  occasionally  and  adding  sulphuric  acid 
to  make  up  for  that  removed  by  copper.  Various  arrange- 
ments were  tried  unsuccessfully,  including  the  use  of  platinum 
black  as  catalyzer. 

The  necessary  oxidation  of  the  iron  can,  however,  be 
easily  secured  in  another  way.  The  solution  of  ferrous  sul- 
phate, resulting  from  the  treatment  of  slime,  which  solution 
should  be  as  hot  and  strong  as  possible,  was  cooled  when 
ferrous  sulphate  crystallized  out.  The  crystals  were  then 
gently  dried  and  roasted,  effecting  a  ready  oxidation  to  basic 


128  LEAD  REFINING  BY  ELECTROLYSIS. 

ferric  sulphate,  without  loss  of  sulphur  oxides.  The  product 
of  basic  ferric  sulphate  was  completely  soluble  in  the  solu- 
tion. 

Roasting  processes. — There  are  two  classes  of  roasting 
processes  for  preparing  slime  for  further  treatment,  one  con- 
sisting in  roasting  the  slime  by  itself,  and  one  with  the  addi- 
tion of  sulphuric  acid.*  Roasted  by  itself  most  slime  ignites 
as  soon  as  it  is  dry,  large  amounts  of  arsenic  fume  escaping 
and  a  yellow  product  resulting,  which  is  largely  unattacked 
by  acid  solutions,  even  hydrofluoric  acid.  The  antimony 
appears  to .  be  converted  to  a  higher  oxide,  which  resists  all 
attempts  to  dissolve  it,  and  the  only  further  treatment  avail- 
able is  by  melting.  Starting  with  slime,  however,  previously 
rather  well  oxidized  by  drying  or  standing  in  the  air,  a  more 
moderate  reaction  with  air  occurs  and  a  less  refractory  pn> 
duct  results.  Even  in  this  case  the  proportion  of  antimony 
soluble  in  HF  as  SbF3  approximates  only  say  60%.  The 
peroxidized  antimony  is  not  appreciably  reducible  by  boiling 
with  acid  ferrous  sulphate  solution. 

Some  slime  can,  however,  be  successfully  oxidized  by 
drying  and  heating  at  a  moderate  temperature,  say  100-150°. 
The  oxidation  is  not  quite  complete.  The  slime  is  next 
treated  with  hot  dilute  sulphuric  acid  and  sodium  nitrate 
added  in  sufficient  quantity  to  complete  the  oxidation.  Cop- 
per and  arsenic  are  thereby  extracted,  and  the  residue  after 
washing  is  leached  with  hydrofluoric  acid  for  antimony-fluo- 
ride. The  drying  and  heating  is  effected  in  long  iron  or  lead 
pans  heated  by  steam  coils  underneath  for  twenty-four  to 
•forty-eight  hours.  The  slime  is  spread  on  in  a  layer  about  4" 

*  E.  F.  Kern,  U.  S.  Patent  803,601.     Nov.  7,  1905. 


CHEMISTRY  OF  SLIME  TREATMENT.  129 

thick,  in  a  lumpy  condition,  as  removed  from  the  filter.  The 
extraction  of  the  copper  and  arsenic  is  best  effected  in  a  lead- 
lined  tank  fitted  with  stirring  gear.  Filtration  may  be  either 
done  in  a  press,  or  on  horizontal  cloth  filters  with  or  with- 
out vacuum  underneath.  Quick  filtration  is  the  best,  because 
no  great  cooling  takes  place,  with  consequent  crystallization 
of  arsenious  acid  or  salts.  On  cooling  the  solution  deposits 
a  little  antimony  trioxide,  and  arsenious  acid  may  crystallize 
out,  if  its  concentration  is  high  enough. 

The  extraction  of  the  antimony  and  treatment  of  the 
solution  is  the  same  as  described  on  page  97. 

Roasting  with  sulphuric-acid  process.  —  This  is  a  simple, 
effective,  and  convenient  method  of  oxidation.  The  first 
step  is  to  mix  the  slime  with  concentrated  sulphuric  acid, 
which  may  be  done  without  drying  the  slime.  The  slime, 
however,  will  either  be  dry,  or  be  in  a  cake  from  some  kind 
of  filter.  The  pasty  or  muddy  mixture  is  then  dried  out  on 
a  plate  or  in  a  furnace  with  free  air  access.  If  sufficient  sul- 
phuric acid  is  used  to  form  lead,  silver,  copper,  bismuth,  and 
antimony  sulphates,  the  product  is  mostly  easily  treated 
later,  probably  because  the  antimony  sulphate,  as  soon  as  it 
touches  water,  decomposes  and  leaves  a  soft  residue,  whereas 
with  less  sulphuric  acid  present  lumps  are  produced  that 
are  with  difficulty  completely  attacked  by  the  solutions.  Dr. 
Valentine  has  suggested  air-drying  first,  followed  by  roasting 
with  sulphuric  acid,  as  saving  acid.* 

In  either  case  acid  fumes  escape  from  the  mixture  on 
adding  H2S04,  which  are  probably  fumes  of  H2SiF6,  or  pos- 
sibly SiF4.  The  smell  of  the  fume  does  not  suggest  HF. 

*  Letter  from  Dr.  Wm.  Valentine. 


130  LEAD  REFINING  BY  ELECTROLYSIS. 

During  the  heating  the  sulphuric  acid  carbonizes  organic 
matter,  a  product  of  the  glue  added  to  the  lead-depositing 
electrolyte,  and  in  some  cases  has  produced  a  product  con- 
taining probably  carbon  in  such  form  as  to  give  the  slime 
a  greasy  flotation.  This  is  probably  the  result  of  the  use  of 
insufficient  H2S04.  As  a  general  average  1  Ib.  of  slime  will 
require  A  to  f  Ib.  sulphuric  acid. 

A  temperature  of  200-250°  C.  for  the  roasting,  which  only 
takes  about  two  hours  with  a  layer  f  inch  thick,  is  about 
right.  As  an  excess  of  sulphuric  acid  is  present  the  pro- 
duct is  never  a  dry,  dusty  mass,  and  no  dusting  has  ever  been 
observed.  The  color  of  the  product  properly  roasted  is  pur 
plish  gray  and  it  consists  of  silver,  lead,  copper,  and  anti- 
mony sulphates  and  gold  and  sulphuric  acid.  In  what  con- 
dition the  arsenic  is  is  not  known,  but  it  is  probably  As203. 
Some  small  amount  of  arsenic  is  probably  volatilized,  but 
the  quantity  lost  is  certainly  small. 

The  destruction  of  gelatine  left  from  the  lead-depositing 
solution  by  the  hot  sulphuric  acid  is  an  advantage,  for  the 
resulting  solutions  settle  and  filter  with  greater  ease  than 
is  the  case  with  other  wet  methods. 

The  product  need  not  be  ground  if  sufficient  sulphuric 
acid  has  been  used.  It  is  boiled  up  with  water,  using  suffi- 
cient to  dissolve  the  arsenic  present.  For  this  prupose  not 
less  than  15  parts  water  should  be  added  for  each  part  of 
arsenic  known  to  be  present.  Considerable  silver  dissolves, 
but  only  from  one-third  to  one-half  of  the  total,  so  no 
attempt  is  made  to  separate  the  silver,  but  copper  is  sus- 
pended in  the  hot  mixture  until  silver  has  been  removed 
from  the  solution.  In  the  filtrate  is  practically  all  the  cop- 
per, 80  to  90%  of  the  arsenic,  and  about  2.5  grams  antimony, 


CHEMISTRY  OF  SLIME  TREATMENT.  131 

and  2  grams  bismuth  per  litre,  if   bismuth  is  present  in  the 
slime. 

Several  methods  of  treating  the  solution  for  arsenic,  cop- 
per, and  bismuth  may  be  adopted,  as  crystallization  for  cop- 
per sulphate  and  arsenious  acid,  precipitation  of  copper  by 
scrap  iron  or  electrolysis  of  the  solution  with  a  lead  anode 
for  electrolytic  copper,  and  an  arsenious  solution,  from  which 
As203,  mixed  with  some  Sb203,  may  be  crystallized.  The 
As203  may  be  further  refined  by  sublimation  or  by  crystalli- 
zation from  hot  water,  to  which  a  little  HF  is  added  to  keep 
antimony  in  solution. 

The  first  method  will  probably  not  easily  yield  copper 
sulphate  free  from  arsenic,  and  I  have  not  attempted  it.  The 
second  method  has  been  in  use  in  practical  work,  but  the 
copper  only  comes  down  slowly  on  scrap  iron,  the  process  is 
wasteful  of  iron  and  acid,  and  the  product  is  a  low-grade  one. 
With  the  third  method  the  cost  of  electrolytic  precipitation 
as  pure  copper  is  less,  the  product  is  a  finished  one,  and  there 
is  no  loss  of  acid,  and  the  separation  from  arsenic  is  nearly 
complete.  The  sulphuric  acid  may  also  be  used  over  again, 
after  concentration. 

In  one  experiment  the  conditions  were  as  follows:  Cop- 
per volume  percentage  on  start  3.5%,  on  finish  0.53%. 
Cathode  current  density  18  to  9  amperes,  and  even  as  low 
as  4.5  for  a  short  time.  Volts  2.3  to  2.1.  Copper  deposited 
at  finish,  good  color.  Anode  of  lead  from  one-quarter  size  of 
cathode  most  of  the  time,  to  same  size  as  cathode.  Current 
efficiency  approximately  100%,  but  not  accurately  deter- 
mined. A  good  agitation  was  maintained,  but  about  the 
middle  of  the  run,  with  current  density  20  amperes,  deposit 
got  black  on  top  for  a  short  time. 


132 


LEAD  REFINING  BY  ELECTROLYSIS. 


The  solution  from  which  copper  was  removed  was  evapo- 
ated  down  until  As203  began  to  crystallize  put,  when  arsenic 
was  mostly  removed  in  hard,  glittering  crystals  intermixed 
with  Sb203  and  some  copper  sulphate,  which  was  washed  out 
with  water. 

A  better  procedure  might  be  to  cool  the  hot  acid  solution 
filtered  from  the  slime,  crystallize  out  copper  sulphate  and 
arsenious  acid,  and  dissolve  the  copper  sulphate  from  the 
product  with  water  or  with  similar  solution  from  a  previous 
treatment  from  which  the  copper  has  been  largely  removed 
by  electrolysis,  leaving  the  crude  arsenic  insoluble.  Any  bis- 
muth present  in  the  hot  solution  from  the  filter,  remains  in 
solution,  as  bismuth  is  as  soluble  or  more  soluble  cold  than 
hot,  except  in  very  strong  acid.  On  evaporating  the  mother 
liquor  down  for  crude  sulphuric  acid  for  the  treatment  of 
another  lot  of  slime,  bismuth  and  remaining  copper  sul- 
phate mostly  separate,  or  can  be  separated  by  cooling  the 
strong  sulphuric  acid. 

The  solubility  of  bismuth  culphate  in  sulphuric  acid  of 
various  strengths  is  approximately  as  given  in  Table  49,  from 
experiments  by  Dr.  E.  F.  Kern: 


TABLE  49. 


.69  grams  Bi  per  100  cc.  cold. 


97% 

55% 

16.6% 

10% 

10% 

3% 

4%      H.SO, 


In   general    bismuth    is    more    soluble    cold    than    hot    in 
weaker  solutions.    Thus   with  20%   H2S04  the   solubility   is 


.61 

100  " 

.19 

100  " 

.22 

100  " 

.21 

100  " 

.16 

100  " 

.10 

. 

100  " 

CHEMISTRY  OF  SLIME  TREATMENT. 


133 


greater  cold;    with  50%  H2S04  and  stronger  acids,  the  solu- 
bility is  greater  hot. 


32%  H2S04  100°  C. 

100°  C. 


.65  gr.  Bi  per  100  cc. 
1.86    "     "     "    100  " 


With  relatively  very  small  amounts  of  bismuth  present 
most  of  it  will  be  removed  from  the  slime  with  the  copper 
and  arsenic.  With  large  amounts  of  bismuth  most  will 
remain  in  the  slime  throughout. 

The  extraction  with  HF  for  antimony  proceeds  as  de- 
scribed under  heading  "Ferric  Sulphate  Process",  page  97, 
but  gives  even  cleaner  extraction  in  this  case.  Some  silver 
dissolves,  which  is  readily  precipitated  out  with  metallic  anti- 
mony. The  following  figures  are  for  Trail  slime  treated 
experimentally.  The  figures  in  the  second  column  are  not 
exactly  right,  probably  partly  on  account  of  absorption  of 
moisture  since  the.  analysis  was  made. 


TABLE  50. 


Slim3 
100  Grams. 

First  Residue 
74  Grams. 

Second  Residue 
33.8  Grams. 

Silver              

14  6% 

12  3% 

20  9% 

Gold    

34  5  ozs. 

8  1% 

Tr 

None 

16% 

Arsenic                               

7  0% 

1  66% 

None 

Antimony.  .           .        

27.60% 

35.9% 

0  56% 

Bismuth  

0.81% 

The  amounts  of  metals  in  the  various  products  are  given 
below.  The  discrepancy  in  silver  is  due  to  the  fact  that  in 
this  experiment  the  silver,  instead  of  being  precipitated  back 
into  the  slime  as  would  be  done  in  practice,  was  precipitated 


134  LEAD  REFINING  BY  ELECTROLYSIS. 

separately  in  the  filtrate  in  order  to  determine  the  quantity 
in  solution. 

TABLE  51. 


In  Slime. 

In  First  Residue. 

In  Second  Residue. 

14.6  gr.  silver 
8  .  1  gr.  copper 
16  .  0  gr.  lead 
7.0  gr.  arsenic 
27  .  6  gr.  antimony 

9.1    gr.  silver 
No  copper 
16        gr.  lead 
1  .  23  gr.  arsenic 
26.6    gr.  antimony 

7.1    gr.  silver 
No  copper. 
16        gr.  lead. 
No  arsenic. 
.  19  gr.  antimony. 

The  extraction  of  copper  by  the  first  solution  was  about 
100%,  of  arsenic  80%,  of  antimony  (from  other  facts),  2.6%. 
The*  extraction  of  arsenic  by  the  HF  is  the  remaining  20% 
of  the  arsenic,  and  of  the  antimony  about  96.6%  of  the  total 
originally  present.  The  result  in  respect  to  antimony  is 
superior  to  that  obtained  by  the  ferric  sulphate  method  on 
dried  slime. 

In  another  experiment  with  600  gr.  lots  of  the  same  slime, 
the  following  results  are  given,  arranged  as  Table  52  (p.  135) 
for  the  sake  of  brevity. 

Dissolving  air-dried  slime  in  H2SiF6  and  HF. — Practi- 
cally all  the  slime,  if  sufficiently  well  oxidized,  dissolves  in 
a  solution  containing  both  fluosilicic  acid,  and  a  moderate 
quantity  of  hydrofluoric  acid,  in  a  few  hours.  Lumps  disin- 
tergrate  of  themselves.  The  solution  resulting  contains  lead 
and  copper  fluosilicates,  antimony  fluoride,  and  arsenious 
acid.  For  the  recovery  of  the  various  metals  experimentally, 
the  solution  was  electrolyzed  first  with  an  antimony  anode 
and  copper  cathode,  current  density  2  amperes  per  square 
foot,  e.m.f.  .25  volts.  Good  copper  comes  down,  if  the  solu- 
tion is  stirred  until  copper  is  nearly  all  gone,  when  the  deposit 


CHEMISTRY  OF  SLIME  TREATMENT. 
TABLE  52. 


135 


Experiment  1. 

Experiment  2. 

Slime  taken.  . 

600  gr. 

600  gr. 

H2SO4  taken  calculated  to  H2SO4  
Sulphuric  acid  lost  in  roasting    percent- 
age of  slime  taken. 

450  gr. 

33% 

400  gr. 

22% 

Copper  removed  from  solution  

By  electrolysis 

By  electrolysis 

Anode  
Copper  in  solution  on  start  
Copper  in  solution  on  finish.  .  .  . 

Lead 
24      gr.  per  litre 
4  Ogr    "      " 

Lead 
21      gr.  per  litre 
2  3gr    "      " 

Quality  of  copper  with  hot  solution 

Varied 

Good 

Water  used  in  dissolving  sulphates.  . 

5   times  weight 

5  times  weight  of 

Amperes  per  sq.  ft.  in  copper  deposition 
maximum 

of  slime 
26 

slime 
9  3 

Amperes  per  sq.  ft.  in  copper  deposition 
minimum.  . 

9  4 

2  2 

Volts,  maximum.     .  . 

2  45 

"      minimum  
CuSO4  crystallized  from  mother  liquor.  .  .  . 
Copper  dissolved  in  precipitating  silver.  .  . 
Wt.  dry  residue  after  dissolving  sulphates 
Antimony  dissolved  to  remove  Ag  from 
fluoride  solution.  ...              .... 

2.0 
18.4gr.4- 
24.5gr.       , 

462      gr. 

7      gr. 

16  gr. 
15  gr. 

12      gr. 

Antimony  deposited  

114      gr. 

149      gr. 

Quality 

Fair    contained 

Excellent        n  o 

Arsenic  in  electrolyte.  .  .  . 

copper        not 
thoroughly 
washed       out 
before     treat- 
ment with  HF 
0.3% 

copper 
0  6% 

Amperes  per  sq.  ft.  cathode  surface,  maxi- 
mum   
Amperes  per  sq.  ft.  cathode  surface,  mini- 
mum 

31.5 
15  6 

24 
4  2 

Amperes  per  sq.  ft.  cathode  surface  at  end 
of  electrolysis. 

16  5 

11  8 

Volts  at  20  amperes  per  sq.  ft.  ...          ... 

2.78 

3  05 

Current  efficiency  
Antimony   as   trifluoride   in   solution   on 
start,  grams  per  litre  
Antimony    as    trifluoride    in    solution  on 
finish,  grams  per  litre  
Antimony    as     pentafluoride    on    finish, 
grams  per  litre  
Free  HF  in  solution  on  start,  grams  per 
litre.  .  .  . 

84.5 
91.4 
7.6 

25  0 

97.5 
108 
6.9 
18.9 
14  0 

Antimony  loss  in  whole  of  two  operations  . 
Insoluble  residue  melted  with  silica,  giving 
clean  dore  weight  

88  gr. 

7.5% 

136  LEAD  REFINING  BY  ELECTROLYSIS. 

turns  whitish.  Analysis  of  copper  product,  91.1%  Cu;  4.8% 
Sb;  .25%  Bi;  no  As  or  Pb.  The  next  product  with  copper 
cathode  and  antimony  anode  is  small  in  amount  and  con- 
sists of  antimony  with  about  10%  copper. 

The  solution  is  next  electrolyzed  with  a  lead  anode  and 
copper  cathode,  current  density  10  amperes  per  square  foot, 
e.m.f.  0.2  to  0.4  volts.  The  antimony  deposit  contained 
90.5%  Sb,  5.6%  As,  no  Cu.  Some  antimony  also  forms  on 
the  anode,  as  scale. 

The  current  density  should  be  .diminished  when  antimony 
is  reduced  to  2%,  to  prevent  lead  from  coming  down. 

The  solution  is  then  electrolyzed  with  lead  anode  and 
cathode.  A  soft  deposit  forms  on  the  cathode,  which  can  be 
compressed  to  solid  metal.  Analyses  show,  for  successive 
products : 

TABLE  53. 

Pb  86.9%  N,d. 

Sb  7.2%  9.2%  4.4%  Trace. 

As  .6%  3.3%  19.6% 

By  reversing  the  current  an  anode  slime  of  arsenic  and 
antimony  may  be  produced. 

The  solution  is  next  electrolyzed  with  carbon  anode  and 
lead  cathode  for  the  production  of  Pb02  and  Pb,  containing 
arsenic  and  antimony  and  free  acid  to  be  used  over  again, 
in  the  treatment  of  another  lot  of  slime.  The  operation  some- 
times succeeds  and  sometimes  no  PbC>2  separates  at  the 
anode,  for  reasons  not  understood. 

The  solution  at  different  times  contained  approximately 
as  follows: 

Column  1  shows  the  solution  after  filtering  from  slime, 
column  2  after  removal  of  copper,  column  3  after  removal  of 


CHEMISTRY  OF  SLIME  TREATMENT.  137 

antimony,  column  4  after  removing  arsenic  and  remaining 
antimony  in  lead,  and  column  5  after  electrolysis  for  Pb02 
and  Pb.  The  Pb02  can  be  put  with  a  charge  of  lead  ore  for 
recovery  of  lead. 

TABLE  54. 

Cu"  1.3%  0     %  0       %          0%  0     % 

Sb'"  5     %  6.6%  .44%  Trace  0     % 

Pb"  5.5%  5.5%  21.5  %  21.5%  5     % 

SiFB"  17     %  17     %  17       %  17     %  17     % 

F  3.5%  3.5%  3.5%           3.5%  3.5% 

As'"  1.1%  1.1%  .88%  Trace  0     % 

Analysis  of  50  parts  of  air-dried  slime  before  treatment 
and  13.5  parts  residue  after  treatment  with  the  mixed  elec- 
trolytes, Table  55. 

TABLE  55. 


Ag  

.   14.6%  



Cu  

•     8.1%  

...     7% 

Pb  

.    16.0%  

...     7.2% 

Sb  

.   27.6%  

...    12.5% 

As  

•     7.0%  

...     1.6% 

Au.. 

The  analysis  of  the  slime  taken  is  not  exact  as  it  had 
probably  absorbed  water,  and  consequently  the  values  may 
be  a  trifle  too  high. 

The  percentage  of  extraction  was  as  follows,  Table  56: 

TABLE  56. 

Copper 73%       extracted. 

Lead 86.2% 

Antimony 87 . 7% 

Arsenic 93 . 8% 

Silver None 

Gold..  " 


CHAPTER  III. 
DEPOSITION   OF   ANTIMONY   FROM  THE   FLUORIDE  SOLUTION. 

THE  electrolytic  refining  of  antimony  with  an  electrolyte 
containing  SbFs  and  HF,  and  perhaps  KF  or  NaF  in  addition,* 
is  a  successful  method,  as  far  as  the  quiet  solution  of  the  anode 
and  good  mechanical  quality  of  the  cathode  is  concerned. 
The  addition  of  KF  or  NaF  is  made  to  increase  the  conduc- 
tivity of  the  solution.  Dilute  hydrofluoric  acid  is  not  as  good 
a  conductor  as  the  other  common  acids,  sulphuric  acid  for 
example.  KF  also  removes  H2SiF6  from  the  solution  as  a 
precipitate  of  K2SiF6.  It  has  been  proved*  that  the  presence 
of  sulphuric  acid  or  sulphates  in  the  refining  electrolyte  (to 
be  distinguished  from  the  electrolyte  when  insoluble  anodes 
are  used,  as  described  later)  prevents  the  easy  solution  of  the 
anodes,  which  is  readily  explained  by  the  ionic  electrochemical 
theory,  as  follows:  The  anion  S04,  with  a  smaller  quantity 
of  the  anions  F'  or  F"2  whichever  is  produced  by  the  disso- 
ciation of  HF,  combine  with  the  anode  metal  to  form  anti- 
mony sulphate  and  antimony  fluoride.  Antimony  sulphate 
is  almost  immediately  decomposed  into  insoluble  antimony 
oxide  or  hydroxide  and  sulphuric  acid,  thus  leaving  an  insu- 
lating coating  on  the  anode,  which  is  only  slowly,  and  in  fact 
too  slowly,  dissolved  off  by  free  HF  which  may  be  present. 


*  Belts    Trans.  Am.   Electrochemical  Society,  Vol.   VIII,  page  190. 

138 


DEPOSITION  OF  ANTIMONY  FLUORIDE  SOLUTION.        139 

This  insulating  coating  actually  exists,  and  may  produce  a 
local  resistance  sufficient  to  absorb  .2  volt  or  more.  As  the 
difference  of  e.m.f.  of  solution  of  copper  and  antimony  in 
the  fluoride  solution  is  probably  considerably  less  than  .1 
volt,  only  a  slight  voltage  drop  is  necessary  to  make  any  cop- 
per present  dissolve  too,  and  once  dissolved,  it  readily  de- 
posits on  the  cathode  with  the  antimony. 

Whether  copper  can  be  left  as  anode  slime,  in  absence  of 
H2S04,  H2SiF6,  etc.,  and  antimony  free  from  copper  can  be 
produced  in  this  way,  has  not  been  definitely  settled. 

Arsenic  probably  dissolves  even  more  readily  than  anti- 
mony and  collects  in  the  solution,  though  some  will  be  found 
in  the  cathode  metal  under  some  conditions,  if  not  all. 

Lead  is  eliminated  satisfactorily,  provided  suitable  cath- 
odes of  other  material  than  lead  are  used. 

Antimony  trifluoride  is  an  extremely  soluble  salt.  Its 
cold  saturated  solution  in  water  has  a  specific  gravity  of  about 
2.6  and  contains  about  three  parts  SbF3  to  1  part  H20.  By 
adding  other  salts  as  sodium,  ammonium,  potassium,  chlo- 
rides, fluorides  and  sulphates,  double  salts  of  less  solubility 
may  be  secured.  Antimony  trifluoride  is  used  as  a  mordant 
in  dyeing,  though  probably  better  results  are  got  with  anti- 
mony lactate  and  tartar  emetic. 

The  deposition  of  antimony  from  the  trifluoride  solution, 
which  in  this  case  may  well  contain  H^SC^  or  sulphates,  is 
important  in  working  up  anode  slime,  as  it  is  often  conven- 
ient to  dissolve  the  antimony  oxide  in  oxidized  slime,  or  slags 
from  melting  slime  in  dilute  hydrofluoric  acid,  followed  by 
deposition  of  the  antimony  from  the  solution.  With  an  in- 
soluble anode  the  principal  reaction  is 


140  LEAD  REFINING  BY  ELECTROLYSIS. 


(1) 

There  is  a  secondary  reaction  that  takes  place,  namely, 
(2)  5SbF3=2Sb  +  3SF5. 

The  last  reaction  is  undesirable,  as  the  antimony  in 
represents  a  loss  of  both  antimony  and  fluorine  as  the  process 
is  worked  at  present.  It  is  hoped  to  devise  means  to  reduce 
this  SbF5  again  to  SbF3,  but  no  serious  attempt  has  been  made 
yet. 

Reaction  2  is  favored  by  high  percentage  of  SbF3,  high 
temperature,  low  percentage  of  H2S04,  large  anode  surface, 
and  ready  access  of  solution  to  the  anode  surface,  so  the  oppo- 
site conditions  are  adhered  to  in  practice,  when  reaction  2 
may  be  reduced  to  about  5%  of  the  whole  electrochemical 
effect. 

The  available  anode  materials  are  platinum,  carbon,  and 
lead.  It  is  quite  possible  that  fine  platinum  wires  would 
make  an  excellent  and  permanent  anode,  but  they  have  not 
been  tried.  Carbon  anodes  of  all  kinds  distintergrate  rapidly, 
and  can  only  be  used  when  the  solution  is  supplied  with 
some  reducing  agent,  as  S02.  This  is  of  course  converted 
at  the  anodes  into  H2S04,  and  might  be  used  practically, 
except  that  it  is  also  reduced  at  the  cathode,  forming  Sb2S3 
Lead  anodes  only  are  actually  used,  but  it  is  necessary  to  use 
them  in  a  special  manner,  both  to  save  lead,  and  to  prevent 
the  formation  of  much  SbF5. 

The  commercial  hydrofluoric  acid  used  in  extracting  an- 
timony from  slime  and  slags  from  melting  slime,  contains 
H2SiF6,  and  as  the  slime  or  slag  usually  contains  silica,  further 
quantities  of  H2SiF6  are  formed.  Dr.  Wm.  Valentine  has 
noticed  that  in  making  HF  by  distilling  fluorspar  with  sul- 


DEPOSITION  OF  ANTIMONY  FLUORIDE  SOLUTION.        141 

phuric  acid,  the  first  HF  to  come  off  contains  most  or  all  of 
the  silica,  and  has  suggested  using  the  first  part  in  making 
lead  refining  electrolyte  and  the  last  in  slime  treating. 

The  presence  of  fluosilicic  acid  (or  any  acid  forming  a  sol- 
uble lead  salt)  is  undesirable,  for  it  acts  on  the  lead  anodes 
as  a  strong  "forming"  agent,  and  therefore  reduces  the  life 
of  the  anodes.  H2SiF6  is  usually  removed  sufficiently  by 
precipitation  with  sodium  sulphate.  Potassium  sulphate 
is  better,  but  its  cost  has  been  too  high.  However,  as  the 


sodium  fluosilicate  is  too  valuable  to  throw  away,  and  should 
be  distilled  with  H2S04  and  a  little  fluorspar  anyway,  to  re- 
cover the  H2SiF6,  potassium  sulphate  would  be  equally  as 
economical,  for  the  residual  potassium  sulphate  could  be  used 
over  again. 

To  test  the  anode  reactions,  antimony  trifluoride  solution 
containing  also  ferrous  sulphate,  to  imitate  conditions  in  prac- 
tice when  iron  gradually  accumulates  in  the  solution,  was  elec- 
trolyzed  in  series  with  a  gas  voltameter,  provisions  being  made 
for  collecting  the  gas  liberated  at  the  anode. 

Apparatus  as  shown  in  Fig.   21a  was  used.     A  is  a 


142 


LEAD  REFINING   BY  ELECTROLYSIS. 


voltameter  using  lead  anode  and  cathode  in  an  acid  solution 

of  copper  sulphate.     B  is  a  resistance  cell  for  regulating  the 

current.     C  contains  the  electrolyte  under  investigation    and 

has   a   small   lead    anode  from    which    the  escaping  gas   can 

be  collected  and  measured  in  the  burette.  The    results   are 
tabulated  in  Table  57. 

TABLE  57. 


I 

No. 

Amperes 
per 
Square 
Foot 

Average 
Voltage. 

Percentage  of 
Current  Used 
in  Generating 

Solution. 

of  Anode. 

Oxygen  Gas. 

1 

87 

3.4 

75.3 

2 
3 

87 
85 

3.4 
3.3 

77 
81.6 

7 
5 

.5gr.  SbF3               ]  per 
gr.  H2S04                100 

4 

86 

3.3 

82.4 

25 

gr.  FeSO4-7H2O  J  cc. 

5 

,    88 

3.2 

71.5 

6 

81 

3.2 

72.7 

7 

87 

3.1 

72.6 

8 
9 

85 
75 

3.3 
3.2 

71.4 
71.7 

15 
40 

gr.  SbF3               }  per 
gr.  FeSO4-7H2O     100 

10 

73 

3.1 

66.5 

5 

gr.  HoSO,            J  cc. 

11 

65 

2.9 

65.1 

12 

45 

2.6 

52 

13 

31 

2.7 

42.5 

The  figures  given  for  percentage  of  current  used  in  gen- 
erating oxygen  gas  give,  by  subtraction  from  100,  the  per- 
centage of  the  current  used  in  oxidizing  ingredients  of  the  so- 
lution, which  is  not  desired.  If  iron  is  oxidized  the  ferric 
salt  will  react  at  the  cathode  and  cut  down  the  efficiency, 
and  any  antimony  oxidized  results  in  temporary  loss  of  anti- 
mony. 

The  highest  efficiency  in  Table  57  is  surpassed  in  prac- 
tical work  with  lead  rods  as  anode,  wrapped  in  several  thick- 
tieSses'(of  cloth  to  prevent  the  free  access  of  oxidizable  salts 
to  the  anode  surface. 


DEPOSITION  OF  ANTIMONY  FLUORIDE  SOLUTION.        143 


The  accompanying  Table  58  shows  the  efficiency  in  ex- 
periments in  depositing  antimony  where  the  efficiency  was 
accurately  determined  and  other  data  carefully  noted. 

In  experiment  2  in  the  table,  no  cloth  was  wrapped  around 
the  anode  rods  and  the  lower  efficiency  should  be  noted. 

TABLE  58. 


No. 

Date. 

Quantity 
Deposited. 

Current  measured 
by 

Anode 
Current  Density 
per  Square  Foot. 

Cathode 
Current  Density 
per  Square  Foot. 

1 

March  1905 

25.7        gr. 

liead   voltamete 

r  375-60    amps. 

25  .  4         amps. 

2 

Sept.     1903 

1.077   kg. 

Ammeter 

180-120 

22.5-15 

3 

Sept.     1903 

.91      " 

75-38 

19-9.5 

4 

Oct.       1903 

.874    " 

100-40 

25-10 

5 

Oct.       1903 

1  .  243    " 

92-52 

23-14 

6 

Oct.       1903 

1.585    " 

105-34 

26-8.5 

7 

March  1907 

114  gr. 

102-51 

31.5-15.6 

8 

March  1907 

149  " 

120-21 

24-4.2 

No. 

Date. 

Sb'"  on  Star 
Efficiency.              in  Solution 

fc        Sb'"  on  Finish 
in  Solution 

Volts. 

per  100  cc. 

per  100  cc. 

1 

March  1905 

90.0%                3.48gr. 

0.80  gr. 

3-2S 

2 

Sept.     1903 

66.5                     6.8 

1.36    ' 

3-2  .  75 

3 

Sept.     1903 

84.5                     5.52 

1.83 

2.9-2.7 

4 

Oct.       1903 

92.9                     5.58 

1.83 

3.15-2.45 

5 

Oct.       1903 

95.4                     7.33 

2.07 

2.9-2.55 

6 

Oct.       1903 

92.0                     8.1 

2.15 

2.9-2.55 

7 

March  1907 

84.5                     9.14 

.76 

3.05-2.78 

8 

March  1907 

97.5                  10.8 

.69 

No. 

Date. 

3b'""   on  Fin- 
sh  in  Solution 
per  100  cc. 

Na2SO4  per       H 
100  cc. 

2SO4  per 
100  cc. 

EbSiFfi  per 
100  cc. 

F'  per  100  cc. 

1 

March  1905 

4 

.66gr. 

4.1     gr. 

2 

Sept      1903 

I  5  er 

4  1 

3 

Sept.     1903 

24  er. 

4  4 

4 

Oct.       1903 

1 

1  gr. 

0  8  er. 

3  2 

5 

Oct.       1903 

.48gr. 

4.5 

6 

Oct.       1903 

1.  gr. 

3.87 

7 

March  1907 

Excess         3 

.  0  gr. 

7.0 

8 

March  1907 

1.89*gr. 

6.45 

*  Total  amount  produced  in  runs  7  and  8  =  approx.  10%. 


144  LEAD  REFINING  BY  ELECTROLYSIS. 

The  anodes  are  of  soft  lead  rods,  usually  J  to  f "  diameter, 
and  covered  with  2  to  4  layers  of  cotton  cloth  to  prevent  the 
access  of  much  SbF3  to  the  actual  anode  surface  with  its  oxidi- 
zing conditions.  Oxygen  escapes  vigorously  while  the  current 
is  on.  The  anode  rods  are  spaced  about  3  inches  apart  in 
rows  with  cathode  plates  between.  An  experimental  tank 
is  described  and  illustrated  on  page  396,  and  a  commercial 
tank  on  page  260. 

The  electrolytic  antimony  may  be  pure  or  not,  according 
to  the  solution  used.  When  lead  cathodes  are  used  the  an- 
timony is  found  to  contain  lead,  the  reason  being  evident 
to  anyone  who  examines  the  corrosion  of  a  lead  cathode,  when 
such  has  been  used.  A  copper  cathode  is  more  satisfac- 
tory. 

The  presence  of  lead  in  the  antimony  is  avoidable  and 
so  is  that  of  copper.  If  the  solution  contains  copper,  it  comes 
down  with  the  first  antimony  deposited,  it  being  necessary 
to  deposit  perhaps  one-tenth  of  the  total  antimony  to  get 
the  copper  all  out.  In  practical  work,  however,  little  or  no 
copper  is  found  in  the  solution  anyway. 

The  removal  of  the  copper  is  better  carried  out  before 
the  electrolysis  in  either  one  of  two  methods,  or  if  the  quan- 
tity is  large,  by  a  combination  of  the  two.  For  considerable 
quantities  of  copper  the  solution  is  electrolyzed  with  antimony 
chunks  as  anode  and  copper  cathodes.  With  a  cathode  cur- 
rent density  of  2  amperes  per  square  foot  and  anode  current 
density,  which  may  be  as  high  as  10  amperes  and  .4  to  .5  volts 
practically  all  the  copper  can  be  got  out  as  good  copper,  while 
of  course  a  corresponding  amount  of  antimony  goes  into  solu- 
tion. For  results  with  this  method  see  Table  59. 


DEPOSITION  OF  ANTIMONY  FLUORIDE  SOLUTION.        145 
TABLE  59. 


No. 

Copper  on 

Start 

On  Finish. 

Anode  C.  D. 
per  Sq.  Ft. 

Cathode  per 
Sq.  Ft. 

Remarks  . 

1 

.24% 

Trace 

About  10 

2 

2 

.50% 

lt 

2-8 

2-8 

Contained    much 

3 

1.00% 

.03 

About  5 

3-2 

H2SiF6 

Small  quantities  of  copper  may  be  conveniently  removed 
by  direct  precipitation  on  antimony.  While  merely  drop- 
ping some  antimony  into  a  tank  containing  the  coppery  solu- 
tion does  little  or  no  good,  an  arrangement  as  shown  in  Fig. 
21&  is  successful,  especially  if  the  solution  passes  through  slowly 


FIG.  216. 

and  at  a  slightly  raised  temperature,  say  40°  C.  The  tank 
contains  broken  antimony  resting  on  a  false  bottom,  in  a  layer 
4"  or  more  thick.  Copper  deposits  on  the  top  of  the  mass, 
while  antimony  dissolves  away  underneath.  The  solution 
escaping  has  a  yellowish  color  and  probably  contains  traces 
of  copper  as  cuprous  fluoride. 

The   removal   of  arsenic   is  not   readily   accomplished   be- 
fore the  electrolysis,  and  the  best  way   seems  to  be  to  let  it 


146 


LEAD  REFINING   BY   ELECTROLYSIS. 


accumulate  in  the  solution,  which  it  may  be  expected  to  do 
in  practice  at  the  rate  of  about  1  part  arsenic  or  less  dissolved 
for  30  parts  antimony  deposited  (see  page  98,  Chapter  II). 
Antimony  deposits  more  readily  than  arsenic. 

For    analyses    of    electrolytic    antimony    from    slime,    see 
Table  60. 

TABLE  60. 
ANALYSES  OF  ANTIMONY. 


No. 

Ag 

Pb 

Cu 

As 

Bi 

Sb 

1 
2 
3 

4 

Nil 

1  1 

1.6% 
.62% 
Nil 
Nil 

2.9% 
•2% 
.07% 
Trace 

2.3% 

'"ii% 

0.5-1.00% 

"•67% 
Nil 

Nil 

93.8% 

No.  1  from  solution  not  purified  from  copper  used  over 
and  over  in  consecutive  treatments  and  deposited  on  lead 
cathodes. 

No.  2  from  slime  containing  much  Bi.  No  refining  of 
solution  from  copper  necessary  in  this  case. 

No.  3  from  solution  purified  of  copper  before  electrolysis. 
Deposited  on  copper  cathodes. 

No.  4  from  commercial  work.  Poorer  quality  also  pro- 
duced. Arsenic  is  hard  to  keep  down. 

In  general,  the  antimony  deposited  will  contain  0.5  to 
1.0%  arsenic,  and  no  easy  method  is  known  so  far  of  produ- 
cing antimony  free  from  arsenic  in  this  way.  However,  ar- 
senic is  about  the  easiest  to  remove  in  the  dry  way  of  the 
metals  we  consider  here.  Arsenic  in  the  presence  of  bases 
is  more  oxidizable  than  antimony  and  can  be  slagged  off  as 
sodium  arsenate  by  fusion  under  soda  in  presence  of  oxidi- 
zing agents. 


DEPOSITION   OF   ANTIMONY   FLUORIDE   SOLUTION.       147 

The  deposited  antimony  is  usually  solid  and  hard,  with  a 
jagged  but  bright  surface.  However,  when  antimony  becomes 
reduced  to  from  1  to  2%,  according  to  the  current  density, 
the  deposit  gets  black  and  soft,  probably  due  to  arsenic  com- 
ing down  too,  and  it  begins  to  fall  from  the  cathodes  as  powder. 
At  this  point,  the  operation  should  be  stopped.  The  de- 
posited antimony  shows  a  tendency  to  peel,  but  does  not  usually 
fall  off  the  cathodes.  It  is  easily  removed  from  the  cathodes, 
particularly  as  these  are  flexible  and  the  brittle  antimony 
separates  readily  on  bending. 

The  deposit  appears  to  contain  some  of  the  solution,  as 
acid  fumes  escape  on  melting,  and  the  metal  loses  slightly 
in  weight. 

As  lead  slime  usually  contains  excess  of  silica,  averaging 
perhaps  1-2%  silica  in  addition  to  some  fluosilicic  acid  or  fluo- 
silicate,  when  antimony  is  extracted  with  HF,  some  silica 
also  dissolves,  varying  in  amount  from  0.9  to  1.8%  calculated 
on  original  weight  of  slime.  By  precipitation  with  sodium 
or  potassium  sulphate  sodium  fluosilicate  is  produced,  which 
can  be  utilized  by  adding  it  in  with  a  charge  of  fluorspar  in 
the  hydrofluoric  acid  plant. 

Cost  of  depositing  antimony  from  the  fluoride  solution 
with  insoluble  anodes. — This  process  has  not  been  used  on 
a  practical  scale  long  enough  for  actual  operating  costs  to 
be  determined,  but  the  cost  can  be  quite  closely  estimated. 
The  tanks  for  practical  work  may  take  4000  amperes,  at  2.8 
to  3.0  volts,  and  are  7  feet  2  inches  long,  2  feet  6  inches  wide, 
and  3  feet  6  inches  deep.  Current,  15  amperes  per  square  foot 
of  cathode  surface.  Anode,  20  sets  of  10  lead  rods,  each  f" 
diameter. 


148  LEAD  REFINING  BY  ELECTROLYSIS. 

TABLE  61. 

Per  Pound 
Antimony. 

Power  cost  at  $50  per  E.H.P.  year  at  95%  efficiency,  1.20  H.P. 

hours  at  $0.00575  ........................................  $0.0069 

Breaking  antimony  from  cathodes  and  labor  cost  operating  tank.  .  0.0010 

Melting  antimony  in  crucibles  and  casting  ....................  0  .  0010 

HF  loss,  mechanical,  5%  ................................  ...'...  0  .  0018 

HF  loss  from  formation  of  H^iF,,  ..............................  0  .  0057 

Na^O^  .12  Ibs.  at  $15  per  ton  .................................  0.0009 

Labor  cost,  precipitating  and  collecting  Na.,SiF6  ..................  0.0010 

Renewals  of  anodes  (in  7  days  3  Ibs.  Sb  deposited  per  ft.  anode  used), 
Smelting  and  refining  and  squirting  0.18  Ibs.  lead  at  $20  per   ton 

including  losses  ..........................................  0  .  0018 

Cloth  and  labor  wrapping  anodes  ..............................  0  .  0020 

Repairs  and  interest  ..........................................  0  .  0020 

Total  .................................................   $0.0241 


Credit  for  Na-jSiF^  added  to  fluorspar  in  making  HF,  yield 

80%  .....................................  ...............     0.0040 

Net  cost  per  Ib,  antimony  deposited  ...........................  $0.0201 


CHAPTER  IV. 

ELECTROLYTIC   REFINING  OF   DORE  BULLION. 

THE  older  nitric-acid  and  sulphuric-acid  processes  are  well 
described  in  various  works  on  the  metallurgy  of  silver  and 
gold,*  to  which  the  reader  is  referred. 

The  electrolytic  processes  are  now  coming  largely  into 
use,  and  it  is  doubtful  if  the  sulphuric-acid  process  will  be 
much  installed  in  future  in  large  works. 

Further  improvements  in  the  electrolytic  processes  may 
be  expected,  particularly  for  alloys  containing  copper,  so  that 
the  sulphuric-acid  process  will  fall  farther  behind  than  ever. 
In  the  older  parting  processes  it  was  desired  to  remove  the 
base  metals  as  fully  as  possible  to  save  acids  in  parting  and 
make  the  process  more  easily  conducted.  This  was  done 
at  quite  high  cost,  and  not  without  losses,  by  cupellation  and 
furnace  treatment,  and  the  practice  is  still  in  vogue  even  at 
plants  using  the  electrolytic  processes,  because  in  that  way 
there  is  required  less  renewals  of  the  electrolytes  to  get  rid 
of  the  accumulating  base  metals  and  keep  the  silver  percent- 
age at  the  necessary  amount.  However,  the  accumulation 
of  base  metals  in  the  electrolyte  need  not  necessarily  be  a 
disadvantage  and  in  the  future  it  will  be  found  better  to  leave 
out  the  furnace  refining  for  bullion  from  anode  slimes,  and 


*Rose,  "Metallurgy  of  Gold";  Eissler^  "Metallurgy  of  Gold." 

149 


150  LEAD  REFINING  BY  ELECTROLYSIS. 

recover  the  base  metals  present  from  the  electrolyte 
instead,  which  it  is  easy  to  do  in  many  ways,  and  will  permit 
greater  economy  than  long  and  expensive  furnacing  with 
unavoidable  metal  losses. 

The  parting  process  of  Dr.  Dietzel*  is  based  on  sound 
principles,  which  ought  yet  to  be  more  largely  applied  in 
better  apparatus.  Alloys  of  gold,  silver  and  copper,  contain- 


Au 5-7%  Zn,  Sn,  Pb,  about  5% 

Ag 22-50%  Cd,  Fe,    Ni,  Pt,  Traces 

Cu 40-65% 

were  successfully  treated  on  a  rather  small  scale. 

The  process  consists  in  electrolyzing  a  solution  of  copper 
nitrate  with  copper  cathode  and  bullion  anode,  separated 
by  a  diaphragm,  copper  depositing  on  the  cathode  of  course, 
and  all  the  metals  except*  gold  dissolving  from  the  anode. 
With  alloys  containing  40%  silver  or  less  I  have  found  it 
difficult  to  dissolve  any  silver  from  hanging  electrodes,  as  the 
other  metals  dissolve  first  and  leave  the  silver  as  a  mushy 
anode  slime,  and  the  same  objection  was  probably  found  by 
Dr.  Dietzel,  as  his  apparatus  has  a  horizontal  conducting  anode, 
of  carbon  probably,  on  which  the  alloy  rests,  and  in  this  way 
of  course  the  silver  may  be  finally  dissolved. 

There  is  maintained  a  continuous  flow  of  copper  nitrate 
solution  to  the  catholyte,  while  the  anolyte  containing  silver 
overflows  and  runs  to  a  precipitating  tank  in  which  the  sil- 
ver is  cemented  out  by  copper,  and  the  solution  then  goes 
back  to  the  electrolytic  cell.  This  system  has  important 
advantages  which  should  not  be  lost  sight  of. 

*  Borchers,  "  Electric  Smelting  and  Refining,"  2d  Eng.  Ed.,  page  304. 


ELECTROLYTE  REFINING  OF  DORE   BULLION.  151 

(1)  The   system  is  perfectly  cyclic    (except   if  the  anodes 
contain  iron,  zinc,  tin,  and  lead),  and  so  little  or  no  mainte- 
nance of  solution  is  required. 

(2)  The  process  is  not  affected  by  variation  in  the  compo- 
sition of  the  anodes,  as  it  will  work  the  same  on  a  series  of 
alloys  all  the  way  from  pure  copper  on  one  end  to  pure  silver 
on  the  other. 

(3)  All  the    silver  is     precipitated   in   one   or  two  tanks, 
and  the  superiority  of  this  .  plan  over  collecting  spongy  silver 
from  a  large  number  of  different  cells  is  apparent. 

(4)  Whatever    copper    is    present   in  the   anodes   appears 
as  electrolytic  copper. 

One  objection,  though  not  readily  apparent,  may  be  noted. 
If  selenium  or  tellurium,  or  other  metal  precipitable  by  copper 
dissolves  from  the  anodes  the  silver  will  contain  that  element. 
This  objection  applies  to  most  precipitation  processes.  Whether 
by  a  partial  precipitation  of  the  silver  the  selenium  or  tellu- 
rium could  be  concentrated  in  a  small  part  of  the  silver,  is  not 
known,  but  it  seems  that  this  probably  could  be  done.  Under 
some  quite  usual  conditions  I  do  not  believe,  however,  that 
selenium  or  tellurium  would  dissolve  with  the  silver.  These 
conditions  are  found  when  the  anode  contains  a  preponderat- 
ing amount  of  silver. 

With  the  Dietzel  process  it  will  be  seen  that  the  silver 
and  copper  solution  escaping  from  the  anode  compartment 
might  be  strong  enough  in  silver  to  provide  electrolyte  for 
an  electrolytic  silver  refining  cell,  while  the  electrolyte  from 
the  latter,  impoverished  in  silver,  might  then  be  carried 
through  the  rest  of  the  process  as  originally  intended.  For 
an  ordinary  Moebius  or  analagous  parting  plant,  the  use  of  a 
number  of  cells  on  the  Dietzel  principle  would  be  desirable, 


152  LEAD  REFINING  BY  ELECTROLYSIS. 

as  providing  a  means  of  recovering  copper  from  and  return- 
ing silver  to  the  electrolyte. 

The  cell  used  by  Dr.  Dietzel  does  not  appear  to  be  espe- 
cially well  suited  to  the  work,  however.  The  use  of  rolling 
cylinders  of  copper  cathodes  would  seem  unnecessary.  For 
most  dore  bullion,  the  percentage  of  silver  is  so  high  that 
the  silver  may  be  cast  directly  to  anodes  and  suspended  or 
supported  in  the  solution,  instead  of  requiring  a  flat  surface 
on  the  bottom  on  which  to  support  the  pieces  of  dore  anc 
the  slime,  still  containing  considerable  silver  in  that  case. 

A  diaphragm  cell  with  diaphragms  of  porous  earthenware 
or  asbestos  sheets  supported  between  perforated  slate  or  glass 
plates,  or  absestos  plugs  in  holes  in  a  wood  partition,  or  one 
of  hardened  asbestos  (see  page  110)  can  all  be  expected  to 
give  a  good  result,  of  which  the  one  objection  is  that  silver 
moves  under  the  action  of  the  current  through  the  diaphragm 
and  toward  the  cathode,  and  interferes  with  the  deposition 
of  a  solid  smooth  cathode.  This  objection  (not  a  very  serious 
one)  can  be  got  around  by  using  a  double  diaphragm  and  in 
the  space  between  a  piece  of  metal,  for  example  copper,  to 
precipitate  silver.  I  have  tried  this  arrangement,  but  the 
results  are  not  conclusive  either  way. 

For  refining  bullion  containing  lead  and  bismuth  appar- 
atus as  shown  in  Fig.  22  gives  good  results.  The  bullion 
is  placed  as  anode  in  cell  1  with  a  lead  cathode  and  a  diaphragm 
of  sulphurized  asbestos  between.  A  steady  flow  of  lead  methyl 
sulphate  solution  containing  5-6%  Pb  and  12-15%  CH3S04, 
is  maintained  to  the  cathode  compartment  in  which  lead 
is  deposited  in  a  fair  condition  of  solidity.  This  lead  is  not 
pure,  however,  and  in  practice  would  go  to  the  lead-bullion 
kettle.  At  the  dore"  anode,  silver,  copper,  bismuth,  and  lead 


ELECTROLYTIC  REFINING  OF  DORE  BULLION. 


153 


dissolve,  provided  the  dore  contains  approximately  70% 
silver  or  over.  If  less  bismuth  and  lead  dissolve  and  leave 
a  mushy  anode  slime  of  silver  containing  about  15%  of  lead 
and  bismuth.  The  solution  continually  overflows  from  the 
cathode  compartment  where  the  percentage  of  lead  is  reduced, 
to  the  anode  compartment,  while  solution  containing  silver, 
lead,  bismuth,  and  traces  of  copper  flows  through  a  series  of 
beakers  to  a  storage  vessel.  The  first  two  contain  pieces  of 


FIG,  22. 

bismuth,  which  cement  the  silver  out  readily,  and  the  last 
two  contain  metallic  lead,  which  throws  out  the  bismuth. 
The  solution,  practically  free  from  copper  and  bismuth,  is  ele- 
vated to  the  higher  storage  tank  and  passes  through  the  series 
again.  The  current  density  in  the  electrolytic  cell  was  15 
amperes  per  square  foot.  Electromotive  force,  2  volts. 

A  process  for  getting  the  silver  into  solution  quickly  at 
the  anode,  without  introducing  any  difficulties  at  the  cathode 


154  LEAD  REFINING  BY  ELECTROLYSIS. 

in  the  way  of  producing  a  solid  deposit  of  silver,  or  lead,  or  cop- 
per, as  the  case  may  be,  is  furnished  by  the  use  of  lead  perox- 
ide and  a  solution  of  fluosilicic  acid,  for  instance.  The  dore 
may  be  dissolved  at  a  veiy  high  current  density  if  the  lead 
peroxide  is  used  as  cathode,  especially  if  the  cathode  is  of 
carbon  electrolytically  coated  with  the  peroxide.  There 
results  a  solution  of  lead,  copper  and  silver  fluosilicates  that 
may  be  rapidly  treated  for  silver  by  precipitation  on  copper, 
while  the  copper  can  be  got  out  by  electrolysis  with  lead  anode 
and  copper  cathode,  and  next  the  lead  can  be  removed  and 
the  lead  peroxide  used  recovered  by  electrolysis  with  carbon 
anode  and  lead  cathode;  or  equally  well,  if  the  dore  contains 
little  lead,  the  precipitation  of  copper  as  mentioned  above 
may  be  omitted,  and  the  solution  containing  copper  and  lead 
fluosilicates  can  be  electrolyzed  with  a  carbon  anode  and-  lead 
cathode  for  electrolytic  copper  and  lead  peroxide,  the  latter 
of  course  being  used  over  again  as  cathode  in  dissolving  more 
bullion. 

In  this  process  there  is  no  difficulty  either  with  the  cathode 
deposits  being  spongy,  or  is  there  need  to  consider  the  dia- 
phragm question,  but  another  difficulty  appears  in  that  the  lead 
peroxide  deposits  on  carbon  electrodes  have  not  yet  been 
dissolved  off  with  high  efficiency,  some  of  the  peroxide  drop- 
ping from  the  electrodes  to  the  bottom  of  the  cell  and  thereby 
escaping  action.  To  obviate  this,  a  plate  of  bullion  or  a  plate 
of  graphite  connected  electrolytically  to  the  peroxide  cathodes 
might  be  placed  on  the  bottom  of  the  cell.  The  peroxide  fall- 
ing on  the  bottom  in  this  case  would  be  ultimately  reduced 
and  dissolved,  though  somewhat  slowly. 

The  electrolytic  refining  of  bullion  has  only  been  practi- 
cally carried  out  with  the  sulphate  and  nitrate  baths,  mainly 


ELECTROLYTIC  REFINING  OF  DORE  BULLION.  155 

the  nitrate,  which  is  in  use  in  several  large  plants  refining 
from  perhaps  20,000  to  100,000  ounces  per  day.  In  either 
case  the  deposited  silver  comes  down  in  a  loose  crystalline 
form.  The  older  Moebius  apparatus  *  is  well  described  and 
illustrated  in  the  patent  specification  and  in  several  avail- 
able works.f  The  more  recent  Balbach  apparatus,:):  im- 
proved by  Mr.  Wm.  Thum,  accomplishes  the  same  result  in  a 
somewhat  different  manner.  The  following  quotation  and  fig- 
ures are  from  Mr.  Easterbrooks'  paper,  §  read  before  the  Ameri- 
can Electrochemical  Society. 

"With  electrolytic  parting  we  have  a  choice  of  two  dis- 
tinct systems  of  depositing  silver  on  the  cathode,  one  in  a 
loose  crystalline  form  at  a  relatively  high  current  density, 
as  in  the  Balbach  and  Moebius  methods,  the  other  with  the 
aid  of  gelatine  in  an  adherent  form  at  a  lower  current  density. 

"The  electrolyte  used  is  a  copper-silver  nitrate  solution, 
although  recently  Betts  ||  has  proposed  using  a  silver  methyl- 
sulphate  solution. 

"These  methods  all  have  in  common  the  characteristic 
of  parting  and  refining  bullion  free  from  gold  and  tellurium 
at  one  operation,  the  deposited  silver  being  melted  and  poured 
into  bars  without  any  further  refining,  as  in  the  sulphuric 
acid  process.  Silver  placed  in  the  tanks  as  anodes  is  not 
handled  until  taken  out  as  refined  silver,  whereas  in  the  acid 
method  the  silver  either  in  solution  or  as  cement  must  be  trans- 
ferred several  times  with  the  aid  of  siphons,  steam,  etc.,  before 


*  U.  S.  patent  310302  and  310533.     Jan.  6,  1885. 

t  Borchers,  "Electric  Smelting  and  Refining,"  2d  Eng.  Ed.;  Watt  and 
Philip's  "Electroplating  and  Electro-refining,"  "Mineral  Industry," 
Vol.  VIII  (1889),  page  337. 

J  U.  S.  patent  588524. 

I  Trans.  Am.  Electrochemical  Society,  Vol.  VIII  (1905),  page  131. 

(I  Electrochem.   Industry,  April,   1905. 


156 


LEAD  REFINING   BY  ELECTROLYSIS. 


it  is  in  a  condition  to  be  melted.  For  these  reasons  it  is  possible 
to  operate  an  electrolytic  parting  plant  with  a  higher  degree 
of  neatness  and  cleanliness  (such  as  the  value  of  the  material 
treated  requires)  than  is  possible  with  acid  parting. 

"A  parting  plant  using  the  Balbach  method  is  simple 
in  construction  and  operation.  Fig.  23  shows  the  cross- 
section  of  a  tank.  The  cathode  is  made  of  one-half  inch  Acheson 
graphite  slabs  fitted  to  the  bottom.  Two  silver  contact-pieces 
rest  respectively  on  the  bullion  to  be  parted  and  the  graphite 
slabs.  Bullion  cast  in  thin  square  slabs  is  contained  in  a  cloth 


FIG.  23. 

case  which  is  supported  on  a  wooden  frame  suspended  over 
the  tank.  The  gold  slimes  accumulate  on  the  under  side  of 
the  bullion,  between  it  and  the  cathode,  increasing  the  resist- 
ance as  the  operation  continues.  Each  tank  has  a  cathode 
surface  of  8  square  feet  and  a  current  density  of  20  to  25 
amperes  per  square  foot  used.*  The  voltage  averages  3.8 
per  tank,  and  an  average  ampere  efficiency  of  93%  was 
obtained  on  a  continued  run,  while  occasionally  an  efficiency 
of  98%  was  secured.  The  power  required  is  31.5  watt-hours 
per  ounce  of  fine  silver  produced. 

"Most   of  the  silver  is  deposited   on  the  cathode   surface 
directly  under  the  anode,  and  the  reduction  of  the  distance 


*The  U.  S.  Metals  Refining  Co.  uses  50  amperes  per  square  foot,  250 
amperes  per  cell.  Engineering  and  Mining  Journal,  May  25,  1907,  page 
1004. 


ELECTROLYTIC  REFINING  OF  DORE  BULLION. 


157 


between  anode  and  cathode  is  limited  by  the  space  necessary 
to  reach  in  and  remove  it,  which  has  to  be  done  frequently 
on  account  of  the  silver  bridging  across  to  the  cathode.  This 
serves  also  to  agitate  the  electrolyte.  There  is  gassing  in  this 
tank  and  the  consumption  of  nitric  acid  is  much  higher  than 
in  the  Moebius  method. 

"At   20   amperes   per   square  foot  about  32%  of  the  daily 
output  of  each  tank  is  held  permanently  in  stock  in  electrolyte 


FIG.  24. 

and  contacts,  which  is  less  than  is  retained  in  the  Moebius 
method. 

"In  Fig.  24  is  shown  the  cross-section  of  a  Moebius 
tank.  They  are  arranged  in  units  of  six  placed  end  to  end, 
each  unit  being  provided  with  apparatus  for  raising  the  boxes 
containing  the  deposited  silver  together  with  the  anodes  and 
cathodes,  and  with  arrangements  for  imparting  a  reciproca- 
ting motion  to  the  wooden  scrapers.  There  is  no  system  of 


158  LEAD  REFINING   BY  ELECTROLYSIS. 

circulating  the  electrolyte,  but  the  scrapers  moving  back  and 
forth  agitate  it.  The  anodes  are  contained  in  a  cloth  frame 
which  holds  the  gold  slimes,  and  the  silver  is  brushed  off  from 
the  silver  cathodes  by  the  wooden  scrapers,  and  drops  into 
a  box  with  hinged  bottom.  It  is  removed  by  raising  the  boxes 
above  the  top  of  the  tanks  and  emptying  it  into  a  tray  placed 
beneath.  This  operation  requires  one-half  hour  per  day  per 
unit.  Each  tank  has  a  cathode  surface  of  about  16.5  square 
feet,  and  a  current  density  of  20  to  25  amperes  per  square 
foot  is  used.  The  voltage  between  electrodes  is  1.4  to  1.5 
and  the  power  cost  is  13.2  watt-hours  per  ounce  of  silver  de- 
posited. An  average  ampere  efficiency  of  94%  is  obtained. 
At  20  amperes  per  square  foot  41%  of  the  daily  output  of 
each  unit  is  permanently  in  stock  in  cathodes  and  electrolyte. 

"The  necessity  of  cutting  out  of  service  the  units  of  a  plant 
using  the  Moebius  method  to  remove  the  silver,  and  the  fre- 
quent siphoning  off  and  replacing  of  portions  of  the  electrolyte  in 
each  tank,  in  both  the  Balbach  and  Moebius  methods,  to  main- 
tain it  of  fixed  compositions,  are  objections  overcome  by  de- 
positing the  silver  on  the  cathode  in  an  adherent  form. 

"This  method  permits  of  an  arrangement  of  tanks  and 
electrodes  and  a  system  of  circulation  of  electrolyte  similar 
to  that  used  in  the  multiple  system  of  copper  refining. 

"The  finely  divided  condition  of  the  gold  in  the  bullion r 
which  in  commercial  work  rarely  contains  more  than  40  parts- 
per  thousand,  requires  the  anodes  to  be  inclosed  in  a  cloth 
frame  to  keep  the  deposited  silver  free  from  gold,  as  the  light, 
fine  particles  do  not  fall  to  the  bottom  of  the  tank  with  suffi- 
cient rapidity.  A  current  density  of  10  amperes  per  square 
foot  is  used,  and  the  power  cost  is  nearly  identical  with  the 
Moebius  method.  Twenty-eight  to  32%  of  the  daily  output 
is  retained  in  cathodes  and  electrolyte." 

The  last  paragraphs  refer  to  the  refining  of  silver  with 
the  nitrate  electrolyte,  with  the  addition  of  gelatine  to  the 
solution,  for  the  production  of  a  solid  cathode  deposit.  Mr. 


ELECTROLYTIC  REFINING  OF  DORE  BULLION.  159 

Easterbrooks  exhibited  some  quite  solid  and  very  brittle  ca- 
thode silver,  with  a  nearly  smooth  surface. 

In  the  Philadelphia  mint,*  dore  bullion  containing  30% 
of  gold  is  now  refined  electrolytically  with  a  solution  contain- 
ing 3%  of  silver  nitrate  and  1J%  of  nitric  acid,  to  which  a 
little  gelatine  is  added.  Each  cell  is  40  ins.  by  20  ins.  and 
11  ins.  deep,  in  which  are  hung  42  anodes  7J  ins.  long, 
2J  ins.  wide,  and  f  ins.  thick,  and  40  cathodes  of  the  same 
width  and  length,  rolled  to  0.016  inch  thickness.  A  current 
density  of  7  amperes  per  square  foot  is  used.  From  the 
above  figures  it  is  apparent  that  an  electrode  separation  of 
3  inches  or  more  must  be  used,  which  is  more  than  would 
be  necessary  if  the  silver  actually  comes  down  solid.  The 
photograph  showed  the  character  of  the  deposit,  which  prob- 
ably consists  of  a  large  number  of  roundish  masses  of  silver 
lightly  fastened  together,  but  with  sufficient  tenacity  to  keep 
from  dropping  into  the  cells  to  any  serious  extent. 

The  Moebius  and  Nebel  process,  using  a  traveling  silver 
belt  to  collect  the  silver,  is  variously  described.!  The  article 
by  Mr.  M.  W.  lies  {  in  "The  Mineral  Industry"  gives  a  rather 
full  description  of  the  plant  with  observations  on  the  amount 
of  nitric  acid  used;  construction  of  the  gold  room;  inventory 
of  gold  and  silver;  action  of  nitric  acid  on  the  silver  belts; 
testing  of  the  solution;  silver  vs.  platinum  contact-points 
for  the  anodes,  and  costs,  as  follows: 


*  Annual  Report  of  the  Director  of  the  U.  S.  Mint,  1905,  abstracted  in 
4 'Electrochemical  and  Metallurgical  Industry,"  1906.  Vol.  IV,  page  306. 

t  English  patent  469  of  1895,  January  8th.  U.  S.  A.  patents  532209 
January  8,  1895;  592097,  October  26,  1897;  "  Electroplating  and  Electro- 
refining, "  Watt  and  Philip,  page  576;  Borcher's  "Electric  Smelting  and 
Refining,"  2d  Eng.  Ed.,  page  323. 

J  "The  Mineral  Industry,"  page  337.     Vol.  VIII. 


160  LEAD  REFINING  BY  ELECTROLYSIS. 

TABLE  62. 

Supnlies.  Per  Month. 

Oil $56.20 

Nitric  acid,  1698  Ibs.  at  7.5  cents 127.35 

Waste,  113  Ibs.  at  9 . 5  cents 10 . 73 

Coal,  25 . 47  tons  at  $2 . 25 57 . 31 

Coke,  1543  Ibs.  at  $9.50 7.32 

Cupels  for  melting  silver 6 . 75 

Crucibles,  2  No.  40  at  $2 4.00 

Sundry  supplies 21 . 12 

$290.78 

Labor.  Per  Month. 

Assistant  superintendent $160 . 00 

Five  men  31  days 379 .  75 

Superintendent  half  time 200 . 00 


$739 . 75 
Interest  $200,000  at  10% $1,666.67 

TABLE  63. 

Cost  per  Ounce  of  Bullion. 

Supplies 0427  cents. 

Labor 1087      ' ' 

Interest .  .  .  2450      ' ' 


Total 3964  cents. 

Royalty 1000      " 


.4964  cents. 

The  article  concludes  with  a  statement  that  the  cost  could 
be  considerably  reduced.  The  rate  of  interest  charged  was 
particularly  high. 

Through  the  kindness  of  the  Compania  Minera,  Fundidora 
y  Afinadora,  Monterey,  Monterey,  Mexico,  Mr.  A.  K.  Brewer, 
Superintendent,  I  am  able  to  give  a  photograph  of  their  parting 
plant,  Plate  3,  and  accurate  information  regarding  it  as  follows: 

Capacity  of  the  plant  is  1000  kilos  =  32, 150  ounces  per 
twenty-four  hours.  The  dore  runs  from  985  to  992  parts 
per  thousand  in  silver  and  gold,  the  gold  making  up  from 
2  to  60  parts  of  the  total.  The  48  tanks  take  250  amperes, 


ELECTROLYTIC  REFINING  OF  DORE  BULLION.  163 

at  2  volts  per  tank,  equal  to  24  K.W.  for  the  whole  plant. 
Five  horse-power  is  used  in  addition  to  drive  the  belts,  revol- 
ing  brushes,  and  solution  pump.  The  circulation  of  the 
electrolyte  is  perfect  and  flows  from  an  upper  storage-tank 
through  the  cells  and  into  a  tank  under  the  floor,  whence  it 
is  raised  by  the  pump  to  the  upper  tank.  To  maintain  the 
solution  a  few  barrels  of  it  are  occasionally  removed,  and 
added  to  the  ore-beds,  so  that  the  values  go  through  the 
smelter. 

The  electrolyte  contains  20-50  grams  silver,  10  to  20 
grams  copper,  2.5  to  15  grams  lead,  and  2.5  to  10  grams  free 
nitric  acid  per  litre.  Nitric  acid  is  added  from  time  to  time 
to  the  solution  in  the  lower  storage-tank  to  maintain  the 
electrolyte  at  working  strength. 

Each  tank  takes  22  anodes  3  ins.  by  12  ins.  by  J  to  J  ins. 
thick,  which  weigh  0.5  to  2  kilos  apiece,  so  that  the  amount 
of  silver  in  the  tanks  is  probably  about  J  to  1  day's  output. 
There  is  no  anode  scrap,  the  anodes  being  totally  dissolved, 
except  the  gold.  The  consumption  of  nitric  acid  is  about 
40  Ibs.  for  32,000  ounces  dore.  Men  required  are  three  day- 
times and  two  at  night,  including  foreman  and  melter. 

It  is  possible  to  form  a  close  estimate  of  the  cost  of  parting 
with  this  apparatus,  on  the  above  results. 

TABLE  64. 

Per  Oz. 

Power  at  $60  per  E.H.P.  year  would  be  * 0190  cents. 

Labor  at  $3  average  * 0470 

Nitric  acid  at  5  cents  per  Ib 0060 

Interest  on  dore  in  tanks  at  85  cents  per  oz 0142 

Interest  on  other  gold  and  silver 0284 

Interest  on  plant,  including  solution 0090 

Fuel  and  materials  for  melting 0100 

Superintendence 0120 

.  1456  cents. 
*  Assumed. 


164  LEAD   REFINING  BY  ELECTROLYSIS. 

The  costs  can  not  be  directly  compared  with  those  given 
below  for  other  methods  because  of  larger  scale  of  opera- 
tions. Refining  20,000  ozs.  per  day,  the  superintendence 
and  labor  items  would  be  quite  a  little  higher  per  ounce,  say 
.019  cents  for  superintendence,  and  .063  for  labor.  Allow- 
ing for  cost  of  new  belts  occasionally,  the  total  cost  on  a 
scale  of  20,000  ounces  per  day  would  approximate  to  .16  to 
.17  cents  per  ounce. 

The  following  description  and  drawing  (Fig.  25)  of  the 
Moebius  and  Nebel  apparatus  are  taken  from  their  U.  S. 
patent : 

Referring  now  to  Fig.  25,  the  letter  A  designates  the  elec- 


FIG.  25. 

trolytic  tank,  made  by  preference  of  a  solid  block  of  wood 
dug  out  and  suitably  lined. 

EB'  are  rolls  adjustably  mounted  in  brackets  placed  on 
the  tank;  CC' ',  an  endless  silver  cathode-belt  passing  over 
the  rolls  BB'. 

W  are  the  shafts  of  the  rolls  BB' ,  mounted  in  brackets 
dd'  and  adjusted  by  screw-bolts  gg',  so  as  to  impart  to  the 
belt  the  proper  tension. 

DD'  are  rolls  to  keep  the  part  C  of  the  belt  immersed  in 
the  bath,  the  roll  D  being  formed  with  teeth,  as  shown,  so 
as  not  too  much  to  press  down  the  silver  precipitated  thereon. 
The  roll  D'  may  have  a  plain  cylindrical  surface. 


ELECTROLYTIC  REFINING  OF  DORE  BULLION.  165 

Slow  motion  in  the  direction  of  the  arrows  is  imparted  to 
the  belt  CCf  by  any  suitable  means,  sueh  as  the  sprocket- 
wheels  Ww  and  chain  m,  operated  by  a  belt-pulley  mounted 
on  the  shaft  s  of  the  small  sprocket-wheel  w. 

T  is  a  circular  brush  held  against  the  belt  while  passing 
over  the  roll  B  and  by  a  weighted  arm  pp',  mounted  loosely 
on  the  shaft  s,  the  brush  being  actuated  from  the  shaft  s  by 
suitable  gear,  so  as  to  brush  the  silver  from  the  belt  into  the 
receptacle  R. 

U  is  an  oil-tank,  within  which  are  mounted  two  rolls  u 
and  r,  both  of  them  a  little  longer  than  the  width  of  the  belt. 
As  shown,  the  oil-tank  is  suspended  from  the  bracket  df  in 
such  a  manner  that  both  rolls  u  and  r  are  continuously  pressed 
against  the  belt.  The  roll  u  is  rotated  by  contact  with  the 
lower  part  Cf  of  the  silver-belt  and  oils  the  surface  of  the 
same,  upon  which  the  silver  is  afterward  deposited  when  in 
the  position  C.  The  roll  r  is  normally  held  by  a  pawl  t  and 
serves  to  remove  or  scrape  off  any  surplus  of  oil.  By  raising 
the  pawl  t  the  roll  r  may  be  revolved,  so  as  to  remove  any 
matter  that  may  have  been  accumulated  thereon.  The 
roll  r  is,  by  preference,  made  of  material  such  as  lamp  wick 
properly  secured  to  the  shaft  in  the  usual  manner.  Any  other 
suitable  oiling  apparatus  may  be  used. 

The  letter  E  designates  one  of  the  anode-cells,  the  anode 
being  connected  to  the  conductor  K,  while  the  belt  is  con- 
nected to  the  conductor  L  by  a  brush  F. 

A  great  many  experiments  have  been  made  in  my  labor- 
atory with  the  aim  of  finding  a  process  by  which  silver  could 
be  refined  in  the  same  manner  that  copper  and  lead  are,  with- 
out the  use  of  any  special  arrangement  to  collect  cement  silver, 
but  to  deposit  solid  silver  on  the  cathodes  at  once. 


166  LEAD  REFINING  BY  ELECTROLYSIS. 

A  number  of  other  objects  were  in  view  at  the  same  time. 
One  was  to  use  a  solution  which  would  take  any  bismuth  in 
the  anodes  into  solution.  Another  was  to  use  a  more  highly- 
conducting  solution  and  use  higher  current  density,  thus  cut- 
ting down  power  and  interest. 

The  best  deposits  were  got  with  a  solution  of  silver  methyl- 
sulphate.  The  deposit  of  silver  was  adherent  and  dense,  but 
not  entirely  solid. 

The  silver  methyl-sulphate  electrolyte  vn  distinction  from 
the  nitrate  electrolyte,  can  be  made  strongly  acid,  and  hence 
highly  conducting,  a  very  important  advantage  in  silver  re- 
fining, as  it  permits  higher  current  densities.  The  other  elec- 
trolytes tried,  of  silver  dithionate  and  fluoborate,  though 
strongly  acid  and  excellent  conductors,  would  not  dissolve 
bismuth  in  quantity  and  gave  somewhat  inferior  results  in 
other  respects. 

Experiments  were  also  made  with  amyl-sulphate  solutions 
strongly  acid  from  amyl-sulphuric  acid,  with  and  without 
the  addition  of  gum  arabic,  etc.,  and  it  appeared  that  there 
was  a  point  to  be  reached  in  respect  to  strength  of  solution 
and  percentage  of  gum  arabic,  etc.,  where  the  deposit  was 
neither  bright  and  loose,  nor  dark  and  soft,  but  smooth  and 
fairly  solid. 

The  deposition  of  entirely  solid  silver  requires  a  delicate 
balance  of  conditions,  and  some  unexplained  phenomena 
must  have  presented  themselves  to  experimenters.  One 
curious  fact  is  that  a  silver  electrolyte  has  to  be  in  use  for 
a  considerable  number  of  hours  before  it  gets  into  good  work- 
ing order  and  the  results  at  the  cathode  strongly  resemble 
those  obtained  in  starting  up  with  a  new  lead  solution,  when 
traces  of  arsenic  and  antimony  come  down  with  the  lead  and 


ELECTROLYTIC  REFINING  OF  DORE  BULLION.  167 

make  it  impossible  to  get  a  solid  deposit.  I  think  it  probable 
that  the  same  thing  occurs  in  the  case  of  silver — that  the 
preparations  of  silver  carbonate,  silver  nitrate,  and  silver 
sulphate,  etc.,  used  in  making  up  solutions,  contain  traces 
of  other  elements  which  deposit  with  the  silver  and  spoil  it 
mechanically.  Possibly  a  trace  of  platinum  is  what  does  it, 
or  perhaps  a  modification  of  silver  itself.  It  is  known  that 
sometimes  more  silver  deposits  than  is  demanded  by  theory, 
and  it  has  been  suggested  that  this  is  due  to  the  deposition 
of  colloidal  particles  of  silver.  In  support  of  the  above  ideas, 
at  one  time  I  prepared  a  solution  for  depositing  silver,  by 
electrolysis  of  the  solution  with  a  silver  anode  in  a  diaphragm- 
cell.  The  resulting  solution  was  one  of  silver  methyl-sul- 
phate, and  gave  a  beautiful  bluish,  smooth,  solid  deposit  of 
silver,  not  inferior  in  structure  to  electrolytic  copper. 

The  use  of  a  higher  anode  current  density,  that  is,  above 
say  20  or  30  amperes  per  square  foot,  is  undesirable  with  the 
methyl-sulphate  solution.  On  one  occasion  a  methyl-sulphate 
solution  that  was  yielding  a  dense  deposit  of  silver  gave  a 
very  poor  deposit  soon  after  the  substitution  of  a  smaller 
and  purer  anode,  the  current  and  cathode  area  remaining  the 
same. 

The  use  of  perchlorate  of  silver,  which  has  been  used  by 
Carhart,  Willard,  and  Henderson  *  in  the  silver  coulomb- 
meter  with  much  better  results  than  were  formerly  obtained 
with  silver  nitrate,  is  analogous  to  the  use  of  methyl-sulphuric 
acid,  as  it  is  also  a  strong  acid  that  can  be  used  in  large  excess 
above  that  required  to  dissolve  the  silver. 

Methyl-sulphuric    acid    is    prepared    by    mixing    together 


*  Am.  Chem.  Soc.,  Vol.  IX,  page  395. 


168 


LEAD  REFINING  BY  ELECTYOLYSIS. 


methyl  alcohol  and  sulphuric  acid.  The  mixture  heats  up, 
and  the  reaction  only  takes  a  short  time.  Previous  results 
that  indicated  a  period  of  eight  to  ten  hours'  reaction  at  100°  C. 
and  statements  in  text-books  to  the  same  effect  are  wrong, 
and  it  is  doubtful  if  the  reaction  takes  more  than  time 
enough  for  mixing. 

I  had  experiments  made  in  my  laboratory  with  various 
mixtures  of  96%  sulphuric  acid  and  88%  methyl-alcohol, 
with  different  heat  treatment.  The  best  results  were  got  by 
simply  adding  the  alcohol  to  the  acid,  mixing  well,  allowing  it 
to  stand  five  minutes,  and  pouring  into  cold  water  (pouring 
on  ice  would  be  better  in  practice). 

The  results  in  that  way  were  as  follows: 

TABLE  65. 


No. 

H2SO4 

Wood  Alcohol. 

1 
2 
3 
4 
5 

20  cc.=35.8  gr;  H.^04 
20  cc.  =  35.8  gr.  H.SO4 
20  cc.  =  35.8  gr.  R^O^ 
20  cc.  =  35.8  gr.  H^O, 
20  cc.  =  35.8  gr.  H.SO, 

15  cc.  =  10.9    gr.  CH4O 
12  cc.=   8.8    gr.  CH4O 
10  cc.=   7.3    gr.  CH4O 
8  cc.=  5.85gr.  CH4O 
6  cc.=   4.4    gr.  CH4O 

No. 

H2SO4  Utilized. 

Alcohol  Utilized. 

1 
2 
3 
4 
5 

48%  of  total 
42%  "     " 
38%"     " 
33%"     " 
30%" 

51%  of  total 

Xf\O7    (i        ii 
OD  /Q 

61%  "     " 
66%"     " 

80%"     " 

With  C.P.  methyl-alcohol,  specific  gravity  .817  =  92%,  the 
result  was  as  follows: 


20  cc.  =  35.8  gr.  H.,SO4 
20  ec.  =  35.8  gr. 
20  cc.  =  35.8  gr. 


TABLE  66. 

12cc.  =  8.9    gr.  CH4O 

10  cc.  =  7.44  gr.  CH4O 

8  cc.  =  5.95  gr.  CH4O 


H2SO4 
Utilized. 

47%  total 

42%     " 
37%     " 


Alcohol 
Utilized. 

61%  total 

65%     " 

72%     " 


ELECTROLYTIC   REFINING   OF   DORE   BULLION.  169 

The  formation  of  water  prevents  complete  reaction.  The 
materials  used  in  the  experiments  already  contained  water. 
With  anhydrous  materials  the  results  must  be  better.  Bet- 
ter results  still  are  got  with  fuming  H2S04,  which  is  now  pro- 
curable at  about  1.3  cents  per  Ib.  for  acid  containing  30% 
of  S03.  EXPERIMENT:  155  grams  fuming  H2S04  containing 
30%  S03,  20  cc.  concentrated  H2S04,  and  75  cc.  wood  alcohol 
88%,  added  together  in  small  portions,  first  one  and  then 
the  other,  starting  with  alcohol  and  ordinary  H2S04,  gave  a 
yield  of  53%  on  the  acid  and  67%  on  the  alcohol.  For  com- 
parison with  the  above  results,  the  proportions  of  S03  and 
alcohol  in  this  experiment  are  the  same  as  with  20  cc.  96% 
H2S04  and  13.5  cc.  alcohol,  when  the  yield  on  acid  is  about 
46%  and  on  alcohol,  say  54%. 

The  course  of  the  reaction  was  traced  by  titrating  a, 
sample  with  ammonia  and  cochineal.  Acid  disappears  in  the 
reaction,  as  one  molecule  of  dibasic  acid  produces  one  molecule 
of  a  monobasic  acid,  and  the  amount  shown  by  titration  to  have 
disappeared  multiplied  by  two  gives  the  amount  of  acid  utilized, 
from  which  can  be  calculated  the  amount  of  alcohol  combined. 

In  practice  the  product  is  poured  on  ice  and  the  liquid 
treated  with  lead  carbonate  (though  lime  or  baryta  would  also 
do)  in  amount  sufficient  to  remove  all  H2S04.  The  filtrate 
from  the  lead  or  calcium  or  barium  sulphate  is  then  treated 
with  silver  carbonate  (from  silver  sulphate  and  soda)  when 
the  solution  is  ready  for  use  if  of  the  right  strength,  namely, 
about  15%  CH3S04'  and  4-6%  Ag. 

Probably  ethyl  alcohol  can  be  used  equally  as  well,  but  con- 
sidering the  relative  molecular  weights  ethyl  alcohol  would 
have  to  be  1.425  times  as  cheap  as  wood  alcohol,  to  compete. 

A  current  density  of  20  to  30  amperes  per  square  foot  is 


170  LEAD  REFINING  BY  ELECTROLYSIS. 

permissible,  and  the  solution,  with  agitation,  may  be  reduced 
to  1.5  grams  of  silver  per  100  cc.  before  it  is  necessary  to 
strengthen  it  up  again.  The  addition  of  gelatine  or  other 
materials  is  not  recommended  at  present,  as  they  are  hard 
to  control  in  their  action  and  the  deposit  is  as  satisfactory 
without.  The  anodes  should  be  wrapped  in  cloth.  Silver- 
plated  and  slightly  greased  graphite  cathodes  may  be  used 
to  advantage,  to  which  the  silver  adheres  though  not  very 
securely.  After  one  day's  refining  the  cathodes  are  removed 
and  the  silver  split  off  and  the  cathodes  returned  to  the  bath. 
As  some  silver  is  likely  to  be  knocked  off  in  the  cells,  the  use 
of  storage-battery  glass  cells  is  convenient.  These  can  be 
handled  and  cleaned  easily,  and  will  take  a  fairly  large  cur- 
rent. A  cell  about  12"  square  and  15"  deep  can  easily  take 
110  amperes,  and  perhaps  as  high  as  200,  while  a  stoneware 
Balbach  cell  about  4  feet  long,  1  foot  defep,  and  2  feet  wide, 
is  only  good  for  about  100,  perhaps  200  amperes,  and  takes 
up  eight  times  the  space. 

The  cost  of  refining  by  the  various  electrolytic  methods  can 
be  estimated  as  follows,  from  various  data.  In  all  cases  the  in- 
terest on  the  original  cost  of  plant  is  taken  at  10%  and  on  metal 
on  hand  at  6%.  It  is  evident  that  the  cost  of  melting  dore  bul- 
lion and  refined  silver  will  be  practically  the  same  in  all  cases. 

Comparative  cost,  refining  20,000  ozs.  per  day,  Table  67. 

TABLE  67 

Cents  per  Oz. 
Moebius.      Balbach.          Betts. 

Interest  on  plant,  including  solution 0090  . 0088  . 0042 

Power  at  $60  per  E.H.P.  year 0146  . 0369  . 0049 

Interest  on  dore,  in  cells  at  $0.85  oz -    .0142  .0142  .0142 

Interest  on  other  gold  and  silver  in  stock .  0284  . 0284  . 0284 

Labor  and  superintendence 0850  . 0850  . 0850 

Chemicals 0100  .0150  .0100 

Fuel  and  material  for  melting 0100  . 0100  . 0065 

.1712          .1983          .1532 


ELECTROLYTIC   REFINING   OF   DORE    BULLION.  171 

The  above  figures  can  be  expected  to  be  fairly  close,  but 
the  fact  that  the  Balbach  method,  as  modified  by  Mr.  Wm. 
Thum,*  has  been  recently  introduced  in  new  plants,  speaks 
against  the  above  figures.  It  is  difficult,  to  see  wherein  the 
new  process  has  the  advantage  over  the  Moebius,  unless  in 
the  matter  of  labor  cost  or  possibly  interest  on  dore  in  the 
cells.  It  seems,  however,  probable  that  the  above  figures  for 
the  Balbach  process  are  a  little  too  high.  One  manager 
remarked  to  me  that  he  thought  the  cost  of  operating  the 
Moebius  and  Balbach  process  about  the  same,  with  the 
advantage  of  simplicity  in  favor  of  the  latter. 

When  it  comes,  however,  to  refining  dore  bullion  con- 
taining important  quantities  of  base  metal,  as  copper,  lead,  or 
bismuth,  the  results  are  somewhat  different,  and  can  be  best 
expressed  by  a  formula  of  the  form 


in  which  A  is  the  cost  of  melting  and  refining  an  ounce  of 
dore  free  from  base  metals,  and  (7,  B,  and  P  are  the  costs  of 
recovering  from  the  electrolyte,  as  marketable  metal,  one 
ounce  each  of  copper,  bismuth,  and  lead  respectively,  and 
adding  the  equivalent  of  silver  to  the  solution,  while  x,  y, 
and  z  are  the  respective  proportions  present. 

In  the  Moebius  and  Balbach  processes  the  cost  of  recover- 
ing bismuth  per  Troy  ounce  from  the  anode  slime  would  app'rox- 
mate  as  follows: 

For  washing  gold  with  soda    to  form  the  soluble  variety  of  bis- 
muth hydrate  or  carbonate,  and  dissolving  in  cold  nitric  acid 


*U.  S.  Patent. 


172  LEAD  REFINING  BY  ELECTROLYSIS. 

heating  the  solution  to  precipitate  basic  nitrate,  about  0.13 

cent  .................................................  0.  13  cent. 

Converting  basic  nitrate  to  metal  by  smelting  with  charcoal, 

about  0.13  cent  ......................................  0.05  " 

Silver  carbonate  to  make  up  for  weakening  of  electrolyte  .......   0.48     " 

Ttoal  ..............................................   0.64   cent. 

For  copper,  copper  nitrate  can  be  crystallized  out  and 
this  could  be  electrolyzed  in  a  dilute  solution  for  copper  and 
nitric  acid,  and  the  nitric  acid  returned  to  the  bath,  though 
this  is  not  probably  actually  done. 

Estimated  cost  per  Troy  ounce  copper  in  bullion  ...............  3  cent. 

If  lead  nitrate  crystallizes  with  the  copper  nitrate,  evi- 
dently the  two  may  be  dissolved  together  and  the  copper  de- 
posited out  with  platinum  or  carbon  anode  as  above,  while 
the  residual  lead  nitrate  can  be  crystallized  from  the  mother 
liquor,  lead  peroxide  being  also  produced,  however. 

Estimated   cost   of   evaporating   lead  nitrate  per  Troy  ounce  and 

corresponding  loss  of  nitric  acid  ...........................  3  cent. 

If  the  dore  should  contain  then  10%  lead,  10%  bismuth, 
and  10%  copper,  the  cost  per  ounce  ought  to  approximate 
to  the  result  given  by  the  formula  above. 


cent. 


With  the  Betts  parting  process  the  values  would  be  some- 
what different,  and  considerably  lower,  for  (1)  there  is  no 
appreciable  loss  of  the  acid  making  the  basis  of  the  electrolyte, 
(2)  no  separate  operation  for  removing  bismuth  from  the 
gold  slime,  and  (3)  the  working  up  of  the  copper-silver  pre- 


ELECTROLYTIC   REFINING   OF   DORE    BULLION.  173 

cipitate  thrown  out  by  metallic  bismuth  and  the  bismuth 
and  copper  thrown  out  by  metallic  lead,  by  treatment  with 
ferric  sulphate,  hot  sulphuric  acid,  etc.,  is  simpler  and  direct. 
I  should  estimate  the  values  for  C,  B,  and  P  at  .5  cent, 
.2  cent,  and  .1  cent,  respectively.  If  these  values  are  realized, 
the  cost  for  the  same  dore  bullion  would  be 

cent. 


These   results   are   not   intended   to   be   entirely   accurate, 
and  of  course  they  can  not  be. 


THE 

UNIVERSITY 

OF 


CHAPTER  V. 

THE    MANUFACTURE    OF    HYDROFLUORIC    AND     FLUOSILICIC 

ACIDS. 

*  "  No  very  useful  literature  on  this  subject  exists  to  the 
best  of  my  knowledge.  Most  chemists  regard  it  as  an  ex- 
tremely dangerous  substance,  and  have  presumably  left  it 
alone  as  much  as  possible.  Yet  hydrofluoric  acid  and  fluo- 
rides have  an  extending  use  for  numerous  purposes.  Its 
preparation  is  easy  and  safe,  if  proper  precautions  are  taken. 

"Samples  of  fluorspar  may  be  tested  by  mixing  say  50 
grams  with  various  proportions  of  66°  sulphuric  acid  in  small 
sheet-iron  pans  and  distilling  under  the  hood.  For  prepara- 
tion in  small  quantities  for  the  laboratory,  apparatus  as  shown 
in  Fig.  26  gives  good  results  if  used  out  of  doors.  The  retort 
is  an  ordinary  cast-iron  pot,  perhaps  one  foot  in  diameter 
and  6  inches  deep.  The  cover  is  made  by  filling  with  sand 
to  near  the  top,  leveling  it  off  and  pouring  in  about  J  inch 
of  lead.  The  lead  pipe  is  separate  from  the  cover,  and  passes 
over  to  a  lead  hydrofluoric-acid  bottle  containing  water.  The 
water  must  not  come  as  high  as  the  end  of  the  lead  pipe. 

"  During  distillation  the  bottle  is  sprayed  with  water  from 
a  hose  to  keep  it  cool.  A  charge  of  about  2  kg.  of  fluorspar 
and  2.5  kg.  H2S04  66°,  is  stirred  up  in  the  pot.  The 

*  By    permission    of    the    Engineering   and    Mining   Journal,  April  20, 
1907. 

174 


HYDROFLUORIC  AND  FLUOSILICIC  ACIDS. 


175 


fluorspar,  for  the  most  part,  dissolves  immediately  on  stir- 
ring in  the  sulphuric  acid,  without  evolution  of  much  fume*, 
until  heat  is  applied.  The  cover  is  put  on  and  dry  cement 
put  over  the  joints  as  a  lute,  cement  being  suitable  for  this 
purpose. 

"The*  heating  should  be  moderate  at  first  to  prevent  too 
much   frothing   in  the   pot.     Distillation  takes  two   or  three 


FIG.  26. 

hours,  and  the  end  can  be  told  by  feeling  of  the  lead  pipe  near 
the  bottle,  which  is  hot  as  long  as  acid  is  coming  over.  Very 
little  loss  is  experienced  and  a  yield  of  80%  or  thereabout, 
is  obtained. 

"  Operation  on  larger  scale. — On  a  large  scale,  the  applica- 
tion of  the  same  principles  is  successful.  The  general  arrange- 
ment is  shown  in  Fig.  27,  for  which  a  few  explanations  are 
necessary.  The  pot  may  be  cast  about  8  ft.  in  diameter,  3  ft. 
deep  at  the  center,  and  1  in.  thick,  with  a  slightly  curving 
bottom  to  prevent  cracking.  For  the  pot  a  cast-iron  cover 
1  in.  thick  is  used,  dipping  into  the  annular  trough  around 
the  pot,  which  contains  strong  sulphuric  acid  as  a  seal.  All 
the  other  seals  are  made  in  the  same  way,  but  water  may  be 
used  for  the  joints  on  the  condensers  where  the  temperature 


176 


LEAD  REFINING  BY  ELECTROLYSIS. 


is  not  so  high.     Lead  retorts  and  lead  covers  for  the  retorts 
are  useless. 

"The  condensers  consist  of  a  series  of  two  or  three  lead 
boxes  of  about  1  cu.m.  capacity,  entirely  submerged  in  a 
water-tank  and  partially  filled  with  water  or  dilute  HF.  Con- 
densers should  be  made  of  heavy  lead,  supported  by  wooden 
pieces  to  which  the  lead  is  attached  by  means  of  lead  straps 
burned  on.  The  lead  delivery-pipes  may  be  about  5  in.  in 
diameter.  The  condensers  have  an  overflow  so  that  the  acid 


FIG.  27. 

never  can  rise  to  the  end  of  the  delivery-pipe.  If  this  hap- 
pened, a  partial  vacuum  might  result,  and  draw  water  back 
into  the  pot,  where  it  would  probably  cause  an  explosion. 

"The  charge  may  consist  of  1000  Ibs.  of  ground  fluorspar 
and  1000  to  1200  Ibs.  66°  sulphuric  acid.  SiF4  comes  off 
first  and  deposits  silica  on  the  water  in  the  first  condenser, 
stopping  absorption  somewhat,  so  that  it  is  necessary  to  stir 
the  water  in  the  first  condenser  until  most  of  the  SiF4  has 
come  over.  The  pot  may  be  charged  in  the  morning  and 
distillation  finished  by  night.  Coal  is  used  for  fuel,  burned 
•on  a  grate  of  about  3  square  feet.  The  residue  in  the  pot  is 
comparatively  hard,  and,  after  cooling,  is  dug  out  with  pick 
and  shovel.  The  yield  of  acid  calculated  on  the  sulphuric 
acid  used  is  approximately  80  to  90%. 

"The  cost  of  manufacture  is  not  great,  the  principal 
items  being  the  raw  materials  necessary.  To  produce  1  Ib. 


HYDROFLUORIC  AND  FLUOSILICIC  ACIDS  177 

anhydrous  HF,  about  2J  Ibs.  of  fluorspar  and  3  Ibs.  sulphuric 
acid  are  necessary.  Fluorspar  and  sulphuric  acid  are  worth 
about  $10  to  $15  a  ton,  making  a  cost  for  raw  materials, 
exclusive  of  coal,  of  approximately  2|  to  4|  cents  per  pound 
anhydrous  HF. 

"Method  of  analysis. — The  sample  of  acid  is  mixed  with 
several  times  its  bulk  of  nearly  saturated  and  neutral  potas- 
sium nitrate  solution.  This  causes  a  precipitation  of  potas- 
sium fluosilicate  in  the  solution:  Phenolphthalein  is  used  as 
indicator,  and  the  solution  titrated  with  caustic  soda  in  the 
cold.  This  gives  the  total  of  the  HF  and  H2SiF6  present. 
The  sample  is  then  heated  to  boiling,  when  it  will  be  found 
that  considerable  more  caustic  soda  may  be  run  in  to  get 
another  end  point.  In  the  first  titration,  the  HF  present  and 
the  HN03  liberated  by  the  reaction  of  potassium  nitrate  and 
fluosilicic  acid  are  neutralized  by  the  alkali.  When  titrated 
hot,  the  precipitated  K2SiF6  is  decomposed  by  the  alkali. 
The  following  is  the  equation  involved: 

K2SiF6 + 4NaOH  =  2KF + 4NaF  +  Si02 ,+ 2H20. 

"The  rule  for  calculating  is,  1  gr.  NaOH  used  in  the  second 
titration  =  0.9  gr.  H2SiF6  in  the  sample.  For  HF  present 
divide  the  number  of  cubic  centimeters  of  NaOH  used  in  the 
second  titration  by  2,  and  subtract  the  result  from  cubic  centi- 
meters used  in  the  first  titration.  The  remainder  shows  the 
HF,  1  gr.  of  NaOH  equalling  0.5  gr.  HF. 

"  Hydrofluoric  acid  has  been  shipped  in  beer-barrels  with 
rosin  lining,  which  are  entirely  successful,  and  last  for  some 
time  and  for  long  shipments;  also  in  rectangular  lead  carboys. 
Its  storage  in  lead  is  not  very  satisfactory  on  account  of  the 


178 


LEAD  REFINING  BY  ELECTROLYSIS. 


corrosion  of  the  lead.  Probably  the  presence  of  sulphuric 
and  fluosilicic  acids  has  some  effect  in  the  corrosion. 

"I  am  indebted  to  Dr.  William  Valentine  for  some  of  my 
data." 

The  conversion  of  hydrofluoric  acid  to  fluosilicic  acid  can 
be  accomplished  in  a  lead-lined  tank  as  shown  in  Fig.  28. 

The  tank  may  be  made  about  5  or  6  feet  square  and  is 
one-third  filled  with  clean  sand  or  broken  quartz.  The  method 
of  operation  is  based  on  the  discovery  that  while  cold  hydro- 


fluoric acid  will  pass  through  sand  and  be  only  partly  con- 
verted to  H2SiF6,  if  the  acid  is  hot,  the  reaction  will  easily 
maintain  the  heat  and  pure  H2SiF6  will  run  through.  Accord- 
ingly on  the  start  the  tank  is  filled  with  water  and  steam  blown 
in  to  heat  it  to  boiling.  When  the  water  running  through 
begins  to  get  hot,  it  is  allowed  to  drain  off,  and  30-35%  acid 
added.  The  tank  is  kept  covered  by  boards,  but  acid  would 
boil  off  in  large  quantities,  except  for  the  addition  of  cold 
water  in  sufficient  amount  to  prevent  this.  As  the  acid  runs 
out  of  the  tank  (one  square  foot  of  sand  at  Trail  used  to'  let 


HYDROFLUORIC   AND   FLUOCILICIC   ACID.  179 

acid  through  at  about  the  rate  of  one  barrel  in  twenty-four 
hours)  more  is  added,  with  enough  cold  water  to  prevent  boil- 
ing off  of  acid.  As  long  as  the  supply  of  acid  is  maintained 
the  tank  will  not  cool  off,  and  the  acid  running  through  has 
only  to  be  diluted  and  have  white  lead  added. 

The  tank  should  be  elevated  so  that  the  products  can  run 
off  into  other  tanks.  At  Trail  the  acid  was  hoisted  to  the 
tank  in  barrels,  the  bung  knocked  in,  and  the  acid  poured 
into  the  tank.  This  was  a  very  disagreeable  job.  A  lead- 
lined  montejus,  if  a  supply  of  acid  under  pressure  is  available, 
would  be  much  better  to  work  with.  When  convenient  the 
hydrofluoric  acid  is  made  on  the  hillside  above  the  works, 
so  that  it  may  be  entirely  managed  by  gravity. 


CHAPTER  VI. 

CHOICE  OF  CONSTANTS. 

THIS  chapter  will  be  a  study  of  the  relative  advantages 
of  various  rates  of  working,  arrangement  of  plant,  methods 
of  slime  treatment,  etc. 

Probably  the  chief  point  to  be  decided  is  the  current 
density  to  be  used  in  depositing  the  lead.  The  problem  can 
be  looked  at  on  many  sides,  but  most  of  these  can  be  elimi- 
nated at  once  as  having  no  real  influence  on  the  result. 

There  is  the  choice  to  be  made  between  the  series  and 
multiple  arrangements  of  electrodes.  The  important  advan- 
tages of  the  two  are  probably  as  follows: 

Series  system. — Power  cost  about  40%-50%  less,  or  a 
saving  of  about  34  K.W.  hours,  worth  about  28  cents  per 
ton. 

No  starting  sheets  required,  or  a  saving  of  about  15-20 
cents  per  ton  over  lead  cathodes,  and  much  less  over  lead- 
plated  steel  cathodes. 

Smaller  construction  cost  for  plant,  excluding  power  plant, 
of  about  $50  per  ton  per  day,  or  at  10%  per  annum  for  in- 
terest, 4  cents  per  ton. 

Total  of  advantages,  about  50  cents  per  ton. 

To  offset  this,  the  multiple  process  will  require  only  about 
half  as  many  anodes  cast  and  charged,  and  will  produce  less 
anode  scrap,  an  advantage  of  10-15  cents  probably. 

180 


CHOICE  OF  CONSTANTS.  181 

No  necessity  of  separating  anode  scrap  and  slime  from 
cathode  lead,  an  advantage  that  might  easily  be  20  cents 
per  ton  and  probably  more,  while  producing  better  refined 
lead,  too.  Less  interest  charge  on  anodes,  which  might  easily 
be  about  5  cents  per  ton.  Total  of  advantages,  35-40  cents 
per  ton,  or  more. 

There  are  probably  other  disadvantages  connected  with  the 
series  system  that  are  only  familiar  to  those  who  have  had 
experience  with  it. 

The  character  of  the  bullion  would  have  to  be  carefully  con- 
sidered in  this  connection.  The  series  process  would  succeed 
best  with  lead  bullion  giving  very  little  slime,  such  as  Missouri 
lead  or  relatively  impure  bullion  containing  1J%  of  antimony 
and  arsenic  or  more.  With  this  latter  kind  of  lead  the  slime  re- 
mains closely  adherent,  and  probably  the  entire  anode  could  be 
dissolved  through  and  the  process  stopped  when  the  cathode 
lead  on  the  other  side  was  being  first  attacked.  The  sljme 
would  remain  as  a  soft,  porous  slab  separate  from  the  cathode 
lead.  With  the  average  grades  of  bullion  containing  little 
arsenic  and  0.5-1%  antimony,  the  slime  is  so  voluminous 
and  soft  that  it  would  be  apt  to  slip  off  the  anode  and  fill 
most  of  the  space  between  the  electrodes,  which  cortdition 
could  perhaps  be  remedied  by  making  the  tanks  nearly  twice 
as  deep  as  the  electrodes,  with  boards  placed  across  the  tank 
every  foot  or  so  to  prevent  the  current  passing  through  the 
bottom  part  to  a  large  extent. 

The  published  information  on  the  series  process  as  applied 
to  copper  is  not  entirely  applicable  to  lead.  One  of  the  great 
objections  to  the  series  system  in  copper  refining  is  the  cost 
of  making  smooth  and  uniform  electrodes.  This  would  be 
much  easier  with  lead,  on  account  of  the  greater  facility  of 


182 


LEAD  REFINING  BY  ELECTROLYSIS. 


melting  and  rolling  it.  The  separation  of  anode  scrap  from 
deposited  metal,  said  to  cost  60  cents  per  ton  with  copper, 
would  not  be  nearly  so  large  an  item  with  lead. 

With  little  probability  of  doing  much  better  with  the  series 
system,  and  some  of  doing  worse,  there  is  little  chance  of  its 
being  attempted,  except  for  small  plants  in  which  it  is  never 
convenient  to  generate  large  currents  of  high  amperage  and 
low  voltage,  or  where  power  is  very  expensive. 

Even  for  small  plants  another  system  proposed,*  which 
combines  to  some  extent  the  advantages  of  the  two  systems, 


is  apt  to  be  better  than  the  series  system.  The  principle  of 
this  arrangement  can  be  easily  noted  from  Fig.  28a. 

With  certain  improvements  in  the  multiple  process  that 
seems  feasible,  and  are  noted  elsewhere,  the  multiple  process 
would  have  a  decided  advantage  over  the  series  process. 

We  have  these  points  to  consider  in  choosing  current 
density: 

(1)  Purity  of  the  lead. — Obviously  the  current  could  be  so 
high  as  to  dissolve  impurities  which  would  deposit  on  the 


*  U.  S.  Patent  789353.     May  9,  1905. 


CHOICE  OF  CONSTANTS.  183 

cathodes.  This  is  not  a  factor  having  any  important  influ- 
ence in  choosing  the  current  density,  as  it  has  been  amply 
demonstrated  that  pure  lead  can  be  produced  over  any  range 
of  current  density  that  is  permissible  from  other  considera- 
tions. 

(2)  Cost  of  glue  used  in  the  solution. — It  seems  probable  that 
the   consumption   of  glue   increases  with  increase   of  current 
to  some  extent.     As   the    amount    of   glue    used    per   ton  of 
lead  produced  is  only  about  one-half  to  three-quarters  of  a 
pound,  it  will  be  seen  that  a  small  increase  or  decrease  of 
this  amount  is  too  small  a  factor  to  be  considered. 

(3)  Low   current   density    means    larger    tank    room    and 
consequently  somewhat  greater  cost  of  building.     Each  am- 
pere per  square  foot  below  12  amperes,  would  make  an  extra 
cost   of    building  of    approximately  $20  per  ton  refined  per 
day,  while  increasing  the  current  up  to  say  20  amperes  would 
save    approximately    $100    per   ton    per    day    on    this    score. 
Capitalized  at  10%,  the  total  difference  between  10  and  20 
amperes  is  only  about  3  cents  per  ton.     In  some  circumstances 

the  value  of  land  will  enter  into  the  question,  but  in  that 

t 

event  it  may  be  better  to  economize  in  space  by  leaving  smaller 
passages  between  the  tanks,  and  making  the  tanks  somewhat 
deeper.  At  the  plant  of  Locke,  Blackett  &  Co.,  Ltd.,  New- 
castle-on-Tyne,  this  method  was  adopted,  and  the  current 
is  12  amperes  per  square  foot,  with  a  space  between  the  rows 
of  tanks  and  around  the  sides  of  about  20  inches.  This  is 
hardly  as  convenient,  but  it  makes  little  if  any  difference  in 
the  cost  per  ton  refined. 

(4)  Interest  on  metal  tied  up. — We  can  calculate  the  thick- 
ness of  metal  dissolved  per  week  at  various  current  densities, 
at  95%   efficiency,   as  follows,  Table  68: 


184 


LEAD   REFINING   BY  ELECTROLYSIS. 


TABLE  68. 


Current  Density  Amperes  per 
Square  Foot. 

10 

12.5 

15 

17.5 

20 


Inches  of  Anode  Dissolved  per 
Week,  on  Each  Side. 

.243 
.305 
.365 
.425 

.486 


The  amount  of  metal  tied  up  may  be  varied  by  varying 
the  thickness  of  the  anodes,  but  it  is,  of  course,  uneconomical 
to  cast  them  very  thin  on  account  of  the  extra  cost  of  casting, 
placing  in  tanks,  cleaning,  etc.  The  best  thickness  of  anode 
is  really  dependent  mainly  on  the  thickness  of  the  cathodes 
it  is  possible  to  make.  Each  set  of  anodes  should  be  made 
so  as  to  give  either  one  or  two  sets  of  cathodes  deposited  as 
thick  as  practicable.  Present  experience  indicates  that  cathodes 
with  about  35  Ibs.  deposited  per  square  foot  are  as  heavy  as 
it  is  desirable  to  make  them.  For  an  anode  yielding  two  sets 
of  cathodes,  and  allowing  15%  for  scrap  to  be  remelted  and 
slime,  makes  a  500-lb.  anode  with  the  usual  size,  2  feet  wide 
and  3  feet  deep.  With  various  current  densities,  bullion 
valued  at  $175  per  ton,  an  average  of  five-sixths  of  the  total 
value  being  in  tanks,  and  allowing  one  day's  supply  unmelted 
cathodes  and  one  in  stock,  and  half  day  for  melting  each,  the 
results  are  as  follows: 

TABLE  69. 


Current  Density. 

Ins.  Dissolved  per 
Week,  Both  Sides. 

Value  of  Metal  on 
Hand  per  Ton 
Refined  per  Day. 

Int.  Charges  per  Ton 
Refined  at  6%. 

10 

.486 

$2570 

$0.423 

12.5 

.608 

2160 

0.355 

15 

.73 

1885 

0.310 

17.5 

.85 

1690 

0.278 

20 

.974 

1550 

0.255 

CHOICE  OF  CONSTANTS.  185 

The  interest  charge  with  the  low  current  density  is  quite 
considerable,  and  could  be  reduced  to  perhaps  two-thirds 
that  amount  by  casting  anodes  one-half  as  thick;  but  the 
extra  c^st  of  casting  and  handling  so  many  more  pieces  would 
leave  little  or  no  net  saving. 

(5)  Depreciation  of  tanks.  —  With  the  wooden  tanks  hitherto 
used,  the  life  of  which  may  be  taken  at  four  years,  and  cost- 
ing $40  each,  evidently  higher  current  density  means  the 
maintenance  of  fewer  tanks  in  a  direct  ratio,  about  as  follows, 
allowing  for  a  certain  amount  of  repairs: 

TABLE  70. 


Current  Density. 

10  $0.143 

12.5  0.114 

15  0.095 

17.5  0.081 

20  0.071 

(6)  At  Trail  the  current  density  is  about  16  amperes  per 
square  foot,  and  the  total  loss  of  acid  is  stated  to  be  10  Ibs. 
of  anhydrous  H2SiFe  per  ton,*  the  solution  containing  6-7  gr» 
lead  and  12-13  gr.  SiFe  per  100  cc.  At  Newcastle-on- 
Tyne  current  density  11  amperes,  the  loss  at  one  time  was 
determined  as  6  Ibs.,  per  ton  of  224®  lbs.;  the  solution  con- 
taining 6  gr.  lead  and  15  gr.  SiF6  per  100  cc. 

The  acid  loss  at  Trail  in  1902  and  1903  was  as  follows: 

TABLE  71. 

August  and  September  16,  1902  13  .  8  Ibs.  SiF6  per  ton  lead. 

September  16-October  6,  1902  7.7    "    SiF6    "      "      " 

January  22-February  13,  1903  6.3    "    SiF6    "      "      " 

*  Communicated  by  Mr.  A.  J.  McNab,  Trail,  B.  C.    See  Appendix. 


186  LEAD  REFINING  BY  ELECTROLYSIS. 

In  the  last  two  determinations  the  current  density  was 
about  12  and  10  amperes  per  square  foot  respectively,  with 
solutions  containing  7.5  gr.  and  8.5  gr.  SiF6  per  100  cc. 
respectively.  These  figures  are  still  too  high  for  good  work, 
as  the  arrangements  for  saving  leaks  and  wash-waters  were 
crude.  This  should  be  noted  especially  for  the  first 
period,  as  operations  had  not  been  at  all  systematized 
then. 

The  use  of  a  high  current  density  would  tend  to  diminish 
acid  loss  from  leaks,  but  there  need  be  no  loss  from  leaks  any- 
way with  good  tanks  and  proper  supports.  The  only  way  in 
which  high  current  density  could  increase  acid  loss  would  be 
by  depositing  silica  in  the  slime  faster  than  the  free  HF  in 
solution  could  dissolve  it,  but  that  means  only  a  loss  of  the 
relatively  valueless  silica,  which  can  be  cured  by  dissolving 
fresh  silica  in  the  solution,  or  by  stirring  the  slime  up  well 
with  the  electrolyte  to  secure  a  recombination  of  silica  and  HF. 
The  latter  simple  and  practicable  procedure  has  not  yet  been 
introduced  in  practice,  as  far  as  I  know. 

Lacking  determinations  of  acid  loss  at  varying  current 
densities,  and  in  view  of  the  facts  we  have  which  do  not  make 
it  seem  probable  that  moderately  higher  current  densities 
would  increase  the  acid  loss,  it  would  not  be  safe  to  speculate 
much  on  the  effect  of  varying  current  density. 

(7)  Interest  on  copper  conductors. — This  is  not  a  variable 
in  respect  to  current  density  to  any  extent,  and  need  not  be 
considered  in  the  present  inquiry. 

(8)  Interest  on  tanks  and  electrolyte  is  a  small  item  of  a 
few  cents  only  and  not  worth  considering  in  this  connection. 
The  difference  in  the  solidity  of  the  lead  and  labor  cost  for 
keeping  tanks  in  good   working  order    is    not  considered  to 


CHOICE  OF  CONSTANTS.  187 

vary  appreciably  with  variation  in  current  density,  within 
the  limits  considered  here. 

(9)  Power. — The  power  cost  per  ton  varies  in  nearly  direct 
proportion  to  the  current  density,  and  also  of  course  with 
the  cost  of  electrical  power,  and  this  latter  may  be  taken  at 
$50  per  E.H.P.  year,  which  seems  a  high  enough  average.  It 
is  now  possible,  by  the  use  of  gas-engines,  water-power,  or 
cheap  coal,  to  generally  reach  or  surpass  this  figure.  It  is  also 
possible  to  secure  wide  variation  in  power  cost,  by  varying 
the  strength  of  the  electrolyte.  Inasmuch  as  even  with  a 
low  current  density  of  say  10  amperes  per  square  foot,  it  is 
economy  to  use  a  rather  strong  solution  containing  about 
16  gr.  SiF6"  per  100  cc.  (except  where  acid  is  unduly  expen- 
sive), my  figures  are  based  on  a  solution  of  7-8  gr.  Pb" 
and  16-17  gr.  SiF6"  for  various  current  densities,  and  also 
for  comparison,  with  a  solution  containing  10  gr.  lead  and 
20  gr.  SiF6.  For  conductivity  determinations,  see  Tables  18 
and  19  and  Figs.  2,  3,  and  4. 

The  temperature  effect,  although  the  conductivity  varies 
quite  a  little  with  change  of  temperature,  is  not  of  much  prac- 
tical importance.  At  Trail  at  one  time  the  electrolyte  was 
heated  as  high  as  50°,  by  a  steam  coil  in  the  circulation-tank, 
but  the  practice  was  found  unsatisfactory  in  several  ways, 
while  the  gain  in  conductivity  was  not  large. 

The  effect  of  temperature  up  to  30°  C.  is  illustrated  in  Figs. 
3  and  4.  The  resistance  was  not  measured  at  higher  tem- 
peratures, but  can  be  safely  calculated  to  about  45°  by  extra- 
polation. But  as,  up  to  the  present,  heating  the  solution 
beyond  30°  C.  has  not  been  a  success,  this  temperature  will 
be  assumed  for  the  purpose  of  calculation.  The  effect  of  the 
current  itself  is  found  to  maintain  the  solution  at  this  tern- 


188 


LEAD   REFINING   BY  ELECTROLYSIS. 


perature  the  year  round,  the  buildings  being  heated  in  winter. 
Electrode  separation  is  taken  as  If  inches,  which  is  permissi- 
ble in  practice.  The  figures  in  Table  72,  are  not  intended 
to  give  the  total  power  cost,  but  only  that  part  of  it  which 
varies  with  variation  in  current  density.  The  other  losses  of 
power,  as  copper  losses  and  contact  losses,  should  be  taken  as 
constant  for  all  current  densities,  for  these  losses  do  not  depend 
on  current  density,  but  on  other  independent  matters,  as  cost 
of  copper  for  bus  bars,  and  cost  of  labor  cleaning  contacts, 
the  economical  balance  for  these  items  being  about  the  same 
regardless  of  current  density.  Power  is  taken  at  $50  per 
E.H.P.  year. 


TABLE  72. 


Current  Density 
Amperes  per 
Square  Foot. 

Volts  from  Re- 
sistance of 
Solution. 

Polarization 
Volts. 

Total  Volts. 

Power  Cost  at 
95%  Efficiency. 

10 

.164 

.02 

.184 

$0  .  352 

12.5 

.205 

.02 

.225 

0.430 

15 

.246 

.02 

.266 

0.504 

17.5 

.288 

.02 

.308 

0.590 

20 

.328 

.02 

.348 

0.665 

The  actual  total  power  cost  for  depositing  is  about 
$0.18  higher  on  account  of  losses  in  conductors  and  con- 
tacts. 

From  Fig.  24,  taking  the  30°  C.  curve,  the  use  of  a  solu- 
tion containing  10  gr.  lead  and  20  gr.  SiFe  per  100  cc. 
would  reduce  the  resistance  from  1.35  ohms  per  inch  unit  in 
the  above  case  to  about  1.05  ohms,  when  the  power  cost  would 
be  somewhat  less,  particularly  for  the  higher  current  densi- 
ties, as  follows: 


CHOICE  OF  CONSTANTS. 
TABLE  73. 


189 


Current  Density 
Amperes  per 
Square  Foot. 

Volts  fiom  Re- 
sistance of 
Solution. 

Polarization 
Volts. 

Total  Volts. 

Power  Cost  95% 
Efficiency. 

10 

0.128 

0.02 

0.148 

$0.280 

12.5 

0.159 

0.02 

0.179 

0.350 

15 

0.191 

0.02 

0.211 

0.392 

17.5 

0.224 

0.02 

0.244 

0.453 

20 

0.255 

0.02 

0.275 

0.511 

Even  stronger  solutions  than  this  I  have  used  in  500-lb. 
runs,  but  the  strongest  solution  yet  used  in  practice  contains 
about  17  gr.  SiF6  per  100  cc. 

Our  final  comparison  will  take  into  account  power  cost, 
depreciation  of  tanks  and  interest  on  metal,  the  other  ele- 
ments entering  into  the  question  being  small  as  far  as  is  known, 
and  may  be  assumed  to  neutralize  each  other: 

TABLE  74. 


Power  Cost. 

Total. 

Current 
Density. 

Tank  De- 
preciation . 

interest  on 
Building, 
Difference. 

Interest  on 
Metal. 

A 

B 

A 

B 

10 

$0.143 

$0.030 

$0.423 

$0.352 

$0.289 

$0.948 

$0.885 

12.5 

0.114 

0.023 

0.355 

0.430 

0.350 

0.922 

0.842 

15 

0.095 

0.015 

0.310 

0.504 

0.392 

0.924 

0.812 

17.5 

0.081 

0.008 

0.278 

0.590 

0.453 

0.957 

0.820 

20 

0.071 

0.000 

0.255 

0.665 

0.511 

0.991 

0.837 

While  there  is  not  much  to  choose,  the  cheapest  current 
density  is  about  15  amperes  per  square  foot.  In  view, 
though,  of  the  slight  differences  in  operating  cost,  the  choice 
of  current  density  will  then  be  largely  influenced  by  other 
factors,  as  first  cost  of  plant  and  elasticity  of  tonnage  treated 
with  the  plant. 


190 


LEAD  REFINING   BY   ELECTROLYSIS. 


From  the  standpoint  of  first  cost  of  plant,  on  one  hand 
we  can  increase  the  tank  capacity  and  cut  down  the  size  of 
the  power  plant,  and  on  the  other,  by  increasing  the  power 
plant  we  can  cut  down  the  cost  of  the  tank  plant.  I  will  assume 
that,  per  ton  refined  per  hour,  the  power  plant  must  furnish 
23.6  K.W.  to  overcome  contact  and  other  metallic  resistance 
anyway  (  =  .1  volt  per  tank  average),  and  a  variable  amount 
of  power  depending  on  the  current  density  as  follows: 


10 

12.5 

15 

17.5 

20 


45.2 
55.2 
65.4 
75.8 
85.8 


TABLE   75. 
K.W. 


68.8  total 
78.8     " 
90.0     " 
99.4     " 
109.4     " 


K.W. 


The  cost  of  power  plant  may  be  roughly  taken  as  $135 
per  K.W.,  and  of  the  tank  plant,  disregarding  handling  ma- 
chinery and  copper  bus  bars  as  practically  constants,  but  includ- 
ing tanks,  electrolyte,  and  floor  area,  at  $15,000  per  ton  per 
hour,  with  a  current  density  of  12.5  amperes. 

Cost  of  variable  items  in  plant  for  solution  with  17  gr. 
SiF6  per  100  cc.: 

TABLE   76. 


Current  Density. 

Power  Plant. 

Tank  Plant. 

Total. 

10 

$  9,270 

$18,750 

$28,020 

12.5 

10,650 

15,000 

25,650 

15 

12,150 

12,000 

24,150 

17.5 

13,400 

10,714 

24,114 

20 

14,750 

9,37', 

24,125 

With    the    stronger    solution,  20  gr.  SiF6    and  10  gr.  Pb 
per  100  cc. 


CHOICE  OF  CONSTANTS. 
TABLE  77. 


191 


Current  Density. 

Power  Plant. 

Tank  Plant. 

Total. 

10 

$7,960 

$20,000 

$27,960 

12.5 

9,050 

16,000 

25,050 

15 

9,370 

13,333 

22,703 

17.5 

10,350 

11,428 

21,778 

20 

11,250 

10,000 

21,250 

From  these  results  it  appears  that  in  future  progress  will 
tend  to  higher  current  densities  and  stronger  solutions,  and 
will  reach  probably  20  amperes  per  square  foot,  if  no  unfore- 
seen objection  crops  up. 

A  plant  built  for  15  amperes  per  square  foot  can  be  arranged 
as  to  be  able  to  stand  a  33%  overload  if  the  solution  is 
strengthened  up  somewhat. 

No  combination  of  current  density  and  solution  strength 
should  be  used,  at  which  a  solid  lead  deposit  may  not  be 
obtained,  otherwise  the  increased  acid  loss  would  offset  any 
advantage  gained. 

Choice  of  slime  process. — Out  of  a  large  number  of  slime 
processes  described  in  more  or  less  detail  in  Chapter  II,  the 
following  only  will  be  considered  as  being  available  at  the 
present  time  for  practical  work,  the  others  being  too  little 
developed  or  to  apply  only  to  special  cases.  The  sodium 
sulphide  process  has  been  given  an  extensive  trial  at  Trail, 
but  full  particulars  have  not  yet  been  given  out.  The  pro- 
cesses considered  below  have  been  the  subject  of  much  experi- 
ment and  have  been  or  will  probably  be  used  in  practical 
work. 

(la)  Melting  with  sulphur  to  matte  and  slag,  especially 
for  slime  containing  little  or  no  bismuth. 


192  LEAD  REFINING  BY  ELECTROLYSIS. 

(16)  Melting  to  dore,  matte,  and  slag,  especially  for  slime 
containing  bismuth. 

(2)  Extraction  of  copper  and  arsenic  in  sulphuric  acid 
solution  and  antimony  from  the  residue  with  hydrofluoric  acid. 
Oxidation  to  be  secured  by  (c)  roasting  with  sulphuric  acid, 
(d)  drying  in  air,  and  (e)  by  ferric  sulphate  produced  elec- 
trolytically. 

Process  (la)  converts  the  copper  and  silver  present  into 
cuprous  and  silver  sulphides,  which  have  to  be  reduced  to 
metal  and  electrolytically  refined.  All  methods  of  converting 
the  matte  into  metal  so  far  successful  are  fairly  expensive, 
and  for  that  reason  this  process  shows  up  at  a  disadvantage 
compared  with  the  others,  when  the  amount  of  silver  and 
copper  are  at  all  large.  But  for  slime  containing  only  a  little 
copper  and  silver  this  process  will  do  excellently.  Assuming 
that  the  lead  bullion  being  refined  contains  50  ozs.  silver  per 
ton  and  0.2%  copper,  beside  20  Ibs.  of  antimony  and  8  Ibs. 
of  arsenic,  the  costs  would  be  about  as  follows,  on  a  large  scale 
of  say  100  tons  of  lead  per  day: 

TABLE  78. 

Per  Ton 
Lead. 

Drying  and  oxidizing  slime  (Fig.  57) $0 . 05 

Melting  in  iron  pot,  coal,  labor,  repairs  (Fig.  58) 0.08 

Sulphur,  2  Ibs 0.03 

Grinding  matte,  heating  with  H^O^  and  melting.     Coal,    labor,   re- 
pairs, H^O* 0.11 

Electrolytically  refining  alloy  for  copper 0 . 04 

Melting  and  refining  silver 0.11 

Grinding  and  leaching  slag  for  SbF3  solution,  and  smelting  and  refining 

PbSO4  residue 0. 12 

Depositing  20  Ibs.  antimony 0 . 40 

$0.94 


CHOICE  OF  CONSTANTS.  193 

Process  (1&).  For  lead  bullion  containing  20  Ibs.  antimony, 
2  Ibs.  copper,  6  Ibs.  arsenic,  2  Ibs.  bismuth,  and  70  ozs.  silver 
per  ton,  the  costs  are  calculated  to  be  about  as  follows: 

TABLE  79. 

Per  Ton 
Lead. 

Drying  and  oxidizing  slime $0 . 05 

Melting  in  iron  pot 0 . 08 

Treating  matte  as  above 0 . 05 

Electrolytically  refining  dore,  and  recovering  bismuth,  copper,  silver, 

and  gold 0.21 

Grinding  and  leaching  slag  as  above 0.12 

Depositing  20  Ibs.  of  antimony 0 . 40 


$0.91 


Usually  slime  will  contain  too  much  copper  for  the  above 
processes,  and  this  would  be  more  certain  in  future  for  elec- 
trolytic refineries,  as  I  will  attempt  to  show.  Very  often 
lead  bullion  as  it  flows  from  the  lead-furnace  contains  copper. 
As  the  smelter  has  not  been  paid  anything  for  copper  in  his 
bullion,  and  can  get  something,  though  nowhere  near  its 
full  value,  if  in  matte,  usually  the  lead  bullion  is  cooled  and 
skimmed  in  the  lead  "  cooler,"  the  dross  with  or  without 
liquating  as  much  lead  as  possible,  going  back  to  the  blast- 
furnace, and  the  copper  being  eventually  recovered  as  a  matte 
containing  probably  on  the  average  40%  of  copper  and  10-15% 
lead.  The  lead  in  this  matte  is  not  usually  paid  for  or  re- 
covered, and  counting  in  the  lead  loss,  the  copper  of  the  dross 
has  been  reduced  in  value  by  as  much  as  6  cents  per  pound. 
In  refining  bullion  by  the  Parkes  process,  the  refiner  has  no 
advantage  over  the  smelter  in  recovering  copper,  as  the  refinery 
also  puts  the  dross  through  a  lead-furnace.  An  electrolytic 
refinery  is,  however,  free  from  these  objections,  and  certainly 


194  LEAD  REFINING  BY  ELECTROLYSIS. 

when  the  smelter  and  refinery  are  under  the  same  control  the 
practice  of  skimming  off  as  much  dross  as  possible  will  be  found 
uneconomical.  Custom  refineries  using  the  electrolytic  pro- 
cesses are  in  a  position  to  credit  the  smelter  enough  for  cop- 
per in  bullion  to  discourage  the  skimming  process.  For  these 
reasons  it  may  be  expected  that  the  tendency  will  be  toward 
more  copper  in  the  bullion,  and  not  less,  so  that  the  consid- 
eration of  bullion  carrying  more  copper,  from  J  to  1%  or  more, 
is  important. 

Probable  cost  of  treating  slime  by  (2c),  from  lead  bullion 
containing  per  ton  20  Ibs.  antimony,  10  Ibs.  copper,  5  Ibs. 
arsenic,  and  70  ozs.  of  silver,  beside  which  5  Ibs.  of  lead  remain 
in  the  slime: 

TABLE  80. 

Per  Ton 
Lead. 

Sulphuric  acid  lost,  15  Ibs $0. 12 

Hydrofluoric  acid  lost 0 . 08 

Operation  electrolytic  tanks,  including  power  at  $50 0 .  4& 

Power,  140  K.W $25.60 

Labor 7.50 

Repairs 2.50 

New  anodes.  .  12 . 20 


Per  day  (100  tons) $47.80 

Repairs  and  supplies 0 . 10 

Melting  and  refining  dore  at  |  cent  per  oz 0.14 

Labor  not  already  included 0.18 

Coal.  .  0.05 


$1 . 15 


If  bismuth  is  present  it  will  be  recovered  from  the  sedi- 
ments deposited  from  the  sulphate  solution,  and  from  the  dore 
bullion,  at  small  cost. 


CHOICE  OF  CONSTANTS.  195 

(2d)  This  process  gives  a  similar  result  and  is  a  little  in- 
ferior, though  the  loss  of  sulphuric  acid  is  less.  On  the  other 
hand  the  roasted  product  is  not  so  readily  leached,  and  some 
sodium  nitrate  is  required  to  finish  the  oxidation. 

(2e)  Ferric  sulphate  process,  for  same  bullion  as  assumed 
for  (2c): 

TABLE  81. 

Per  Ton 
Load. 

Operation  of  electrolytic  tanks,  including  power  at  $50  per  year.     Cop- 
per tanks  operate  at  1.75  volts  and  antimony  tanks  at  2.9  volts, 

with  90%  efficiency  each $0.63 

Power,  175  K.W $32.40 

Labor 10 . 00 

Repairs.  .-...' 12 . 50 

New  anodes.  .  8 . 00 


Per  day  (100  tons) $62 . 90 

Hydrofluoric  acid  loss,  1  Ib.  at  7.5  cents 0.08 

Sulphuric  acid,  10  Ibs 0 . 08 

Melting  and  refining  dore  at  ^  cent 0.14 

Labor  not  already  included 0 . 24 

Repairs  and  supplies 0.10 

Coal  for  melting,  roasting  matte,  melting  antimony 0 . 03 


$1.30 

Credit  for  30  Ibs.  copper  recovered  from  matte 1 . 05 

Cost $0.25 

If  bismuth  is  present,  it  will  be  recovered  in  a  special  bullion 
from  smelting  the  leached  matte,  and  to  a  small  extent  in 
the  dore  bullion. 

The  above  results  do  not  include  superintendence  and  assay- 
ing, metal  losses,  or  interest  on  plant,  but  the  comparison  is 
still  valid; 


196  LEAD  REFINING  BY  ELECTROLYSIS. 

In  a  general  way,  the  ferric  sulphate  method,  beside  being 
the  most  economical  in  net  operating  cost,  is  the  cleanest, 
easiest,  and  quickest,  and  will  cause  less  loss  of  precious  metals 
through  the  various  channels  of  loss,  for  the  slime  is  not  dried 
at  all  until  the  final  melting  to  dore  bullion.  The  ferric  sul- 
phate method  will  recover  all  the  precious  metal  values  shown 
by  corrected  fire  assay,  or  more. 


CHAPTER  VII. 

REFINERY    CONSTRUCTION,    OPERATION,    AND    REFINING. 

COSTS. 

THE  general  arrangement  of  most,  if  not  all,  large  elec- 
trolytic copper  refineries  is  on  the  one  level  plan  with  indus- 
trial railway  running  between  the  different  departments,  motive 
power  being  generally  provided  by  electric  locomotives.  This, 
arrangement  can  be  safely  copied  for  electrolytic  lead  refineries.. 
In  the  casting  plant  the  molds  to  receive  melted  metal  may 
be  on  a  level  a  few  feet  below  the  general  level;  but  in  stacking 
the  anodes,  ready  to  be  carried  off  by  the  tank-load  by  the 
electric  cranes,  they  can  be  easily  hoisted  the  necessary  few 
feet. 

In  considering  the  level  question,  the  tank-room  can  be 
regarded  as  receiving  and  delivering  material  on  the  same 
level. 

The  melting  plant  should  be  so  situated  and  arranged 
that  lead  and  bullion  may  be  handled  from  and  to  the  railroad 
cars  as  simply  as  possible.  In  order  to  deliver  the  cast  anodes 
and  pig  lead  on  nearly  the  same  level  as  the  tank-house  and 
shipping  track,  it  is  preferable  to  have  the  melting-furnaces 
at  a  higher  level,  so  that  the  metal  may  flow  by  gravity  through, 
siphons  to  the  molds.  If  a  Rosing  steam  pump  is  used,  the 
pots  may,  of  course,  be  brought  down  to  the  same  level;  but 

197 


198 


LEAD  REFINING  BY  ELECTROLYSIS. 


this  has  been  tried  at  Trail  and  I  believe  not  found  entirely 
satisfactory.* 

The  melting  of  the  bullion  bars  and  anode  scrap  and  of 
the  cathodes  has  been  done  up  to  the  present  by  simple  melt- 
ing down  in  kettles.  The  cathodes  are  wet  when  they  come 
from  the  refinery  and  have  to  be  dried  before  coming  into  con- 
tact with  melted  lead  in  the  pot.  The  usual  plan  is  to  pile 
the  cathodes  high  above  the  pot  and  melt  down  slowly.  A 
cover  and  pipe  should  be  provided  over  the  kettle  to  carry 
off  fumes.  When  the  lead  is  melted  finally  about  4%  of  dross 
floats  on  top,  which  is  skimmed  off  by  hand,  a  slow  and  labori- 
ous method.  A  Howard  skimmer,  such  as  used  in  the 
Parkes  process,  to  take  off  the  dross,  would  be  a  desirable 
adjunct.  Plate  4  shows  the  Trail  melting  plant,  1903-1904. 

The  dross  ordinarily  produced  is  less  pure  than  the  lead 
and  contains  more  silver.  Table  82  shows  the  comparative 
analyses  of  lead  and  dross  from  the  same  meltings  at  Trail. 

TABLE  82. 


Fe 

Cu 

As 

Sb 

Zn 

Ag.  Ozs 

Lead.         

0010% 

.0003% 

.0002% 

.0010% 

None 

Dross 

0016% 

.0005% 

.0003% 

.0016% 

(  < 

Lead  

0008% 

.0009% 

.0001% 

.  0009% 

(  t 

.24 

Dross  

.0011% 

.0010% 

.0008% 

.0107% 

1  1 

I  believe  that  the  present  method  of  melting  the  cathodes 
is  capable  of  considerable  improvement,  along  the  line  of  sav- 
ing labor,  and  making  little  or  no  dross.  The  piling  of  the 
cathodes  above  the  pot,  and  the  necessity  of  steering  them 


*  See,  however,  description  of  lead  pumps  in  Appendix  I. 


PLATE  4. 
TRUSAVELL  ANODE  MOLD  AND  ANODE. 


page  199 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     201 

into  the  pot  properly  as  the  charge  settles  down,  requires  some 
labor,  as  does  the  handling  of  the  dross.  What  is  wanted  is 
to  dump  the  damp  cathodes  by  the  carload  and  have  no  more 
labor  involved  until  the  lead  is  cast.  This  end  could  be 
achieved  by  dumping  the  cathodes  through  the  roof  of  a 
preheating  reverberatory  furnace  at  a  level  just  above  that 
of  the  refined-lead  kettle.  The  reverberatory  could  have  a 
cast-iron  or  steel  bottom  to  prevent  its  being  broken  up  by 
the  falling  lead. 

A  very  small  heat  supply  will  suffice  to  melt  lead  in  this 
way,  and  if  the  furnace  gases  were  kept  reducing  at  the  same 
time,  little  or  no  dross  would  be  formed  from  oxidation  of  the 
melting  cathodes.  At  50%  heating  efficiency,  which  does  not 
seem  high  for  a  furnace  working  at  the  melting-point  of  lead, 
8  Ibs.  of  coal  would  be  theoretically  required  to  melt  a  ton 
of  lead.  The  waste  heat  from  the  bullion  or  refined-lead  ket- 
tles could  be  applied  very  easily  to  the  melting  in  the  rever- 
beratory. A  similar  operation  is  the  liquation  of  bullion  in 
a  reverberatory,  to  soften  it  for  the  Parkes  process,  which 
requires  with  a  35-ton  furnace  24  Ibs.  of  coal  per  ton  of  lead 
melted.*  The  objection  might  be  raised  that  the  resulting 
lead  will  be  slightly  less  pure,  which  is  undoubtedly  a  fact. 
Electrolytically  refined  lead  usually  contains  from  .1  to  .5  ozs. 
of  silver,  which  is  in  practical  work  almost  entirely  due  to 
slime  not  washed  off  the  surface  of  the  cathodes.  In  taking 
a  crop  of  cathodes  from  a  tank,  the  disturbance  of  the  tank 
or  unavoidable  contact  of  the  anodes  and  cathodes,  is  apt 
to  loosen  some  slime  from  the  anodes  and  get  part  of  it  on 
the  cathodes.  When  these  are  dipped  in  muddy  wash-water,  as 

*  Collins,  "The  Metallurgy  of  Lead,"  page  288. 


202  LEAD  REFINING  BY  ELECTROLYSIS. 

is  sometimes  done,  the  result  is  an  even  distribution  of  part  of 
the  slime  over  the  surface.  In  the  ordinary  melting  quite  a 
little  of  this  slime  goes  into  the  dross,  as  will  be  seen  from 
Table  83,  from  the  United  States  Metals  Refining  Company. 

TABLE  83. 

Lead 25    ozs.  per  ton. 

Dross  20  mesh  oversize 1 . 836  "  "  " 

11  40  "  "  1.776  "  "  " 

"  60  "  "  1.75  "  "  " 

"  though  60  mesh 3.66  "  "  " 

Assuming  4%  of  dross  reduced  and  melted  into  the  lead, 
the  lead  would  have  carried  approximately  .35  ozs.  instead 
of  .25  ozs.  of  silver,  provided  all  the  adherent  slime  was  taken 
up  by  the  lead,  which  is  not  probable,  as  some  of  the  slime  would 
probably  remain  in  the  furnace  as  dross.  The  difference  in 
the  amount  of  the  other  impurities  in  the  lead  would  be  too 
small, to  be  noticeable. 

For  a  combined  smelting  and  refining  works,  the  lead 
should  be  cast  from  the  blast-furnaces  into  anodes  direct. 

In  refineries,  anodes  are  cast  in  open  molds  lying  in  a  semi- 
circle in  front  of  the  pot,  to  which  the  usual  lead  launder 
reaches  from  the  discharge  end  of  the  siphon  or  pump.  These 
may  be  seen  mounted  on  a  long  car  in  the  photograph  of  the 
Trail  melting  plant  of  several  years  ago,  Plate  5. 

The  use  of  a  rotating  table,  on  which  the  molds  are  placed, 
similarly  to  the  casting  machinery  used  in  electrolytic  copper 
works,  has  been  proposed,  but  it  is  doubtful  if  it  would  save 
anything  in  cost  of  casting.  It  is  quite  possible  that  the 
adoption  of  rotating  molds  in  casting  copper  anodes  was  a 
necessity,  because  copper  could  not  be  conveniently  run  through 
a  long  launder  to  a  semicircle  of  molds,  and  copper  requires 


EEFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     203 


so  much  cooling  that  it  is  necessary  to  pass  the  casts  under 
water,  so  the  successful  use  of  rotating  molds  in  copper  cast- 
ing is  no  valid  argument  for  its  adoption  in  lead  casting. 

An  anode  mold  is  shown  in  Fig.  29.  The  following  re- 
marks will  be  of  value  in  designing  them.  No  draft  is  pro- 
vided at  the  under  side  of  the  lug.  The  sides  of  the  lug 
should  not  be  too  steep,  as  the  anode  in  contracting  draws 


r- 


*-4t-"- 


2H6- -»' 


+mf. „ 


FIG.  29. 


the  lugs  against  the  mold  at  those  points,  making  the  anode 
stick  in  the  mold  so  that  it  has  to  be  forced  out.  Except  on 
the  under  side  of  the  lugs,  which  are  required  flat  to  make  the 
anode  hang  straight  in  the  tank,  a  good  draft  may  as  well  be 
provided  as  not,  to  facilitate  the  removal  of  the  anodes  with- 
out its  being  necessary  to  pry  them  out. 

No  trouble  from  sticking  is  experienced  at  the  under  side 
of  the  lugs,,  as  the  anode  contracts  somewhat  after  it  has  solidi- 


204  LEAD  REFINING  BY  ELECTROLYSIS. 

fied.  Once  in  a  while  the  anode  molds  should  be  sprinkled 
with  clayey  water,  which  rapidly  dries  off  the  hot  iron,  and 
leaves  a  coating  to  which  the  lead  cannot  stick.  The  block 
at  the  top  between  the  two  lugs  is  separate  and  removable, 
and  gives  a  place  to  put  a  bar  in  to  lift  the  anode  slightly  from 
the  mold,  so  that  it  may  be  engaged  by  hooks.  A  com- 
pressed-air hoist  on  a  light  jib-crane  enables  one  man  to  lift 
anodes  and  stack  them  rapidly. 

The  anodes  molded  in  the  way  mentioned  suffer  from 
irregularities  of  form  or  weight,  as  would  naturally  be  ex- 
pected when  the  workman's  sole  means  of  judging  the  amount 
of  metal  run  into  each  mold  is  by  eye.  Then  the  molds  and 
inflowing  bullion  are  at  various  accidental  temperatures,  so 
there  can  be  no  uniform  procedure  for  getting  the  right  amount 
of  metal  in  the  lugs  and  all  the  different  portions  of  the  plates. 
Even  if  the  mold  is  perfectly  level  an  anode  may  average 
considerably  thicker  on  one  end  than  the  other  from  the  unequal 
flow  and  chilling  of  the  lead.  When  these  irregularly-formed 
plates  are  suspended  in  the  tanks  the  thinnest  plates  will  be 
entirely  dissolved,  while  considerable  metal  remains  on  some 
of  the  others,  increasing  the  proportion  of  anode  scrap  to  be 
remelted.  A  stiffening  rib  about  J  inch  deep  and  2  inches 
wide  is  usually  cast  across  the  top  of  the  anodes  to  prevent 
their  collapsing  and  falling  in  the  tank  at  the  end  of  the  run 
when  the  metal  has  been  nearly  all  dissolved.  Part  of  the 
rib,  of  course,  remains  when  all  of  the  lower  part  of  the 
anode  has  been  decomposed. 

For  the  best  work  and  highest  efficiency  in  the  tanks,  the 
anodes  should  all  be  of  the  same  weight,  and  slightly  thicker 
at  the  top  than  at  the  bottom.  For  these  reasons  the  idea 
of  using  closed  molds  for  casting  the  anodes  has  been  an  attrac- 


*  8 
§  1 


PLATE   6 
TRUSWELL  ANODE  MOLD 


page.  207 


UNIVERSITY 

OF 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     209 

live  one.  The  closed  molds  should  aim  preferably  to  cast  the 
anodes  bottom  up  so  that  the  dross  rising  in  the  cooling  liquid 
metal  can  not  flow  into  the  lugs,  both  weakening  them  and 
sending  the  impurities  back  to  the  melting-kettle  in  greater 
relative  amount  than  they  exist  in  the  bullion.  With  anodes 
cast  in  closed  molds  experimentally,  the  tank  efficiency  has 
been  raised  at  Trail  to  95%,*  as  against  the  usual  90%.  Mr.  R. 
Truswell,  Trail,  B.  C.,  has  applied  for  United  States,!  Canadian, 
and  English  patents  for  his  anode-mold,  which  is  shown  in 
the  photographs  supplied  by  Mr.  Truswell,  Plates  5  and  6. 
The  following  description  is  from  Mr.  TruswelFs  article :{ 

"The  illustrations  show  a  new  mold  that  I  have  devel- 
oped for  the  purpose  of  casting  anodes;  it  has  the  advan- 
tage that  the  plate,  being  enclosed  during  the  process  of  cast- 
ing, will  be  of  uniform  thickness  and  not  liable  to  be  warped 
or  twisted.  To  prevent  the  dross  or  spongy  characteristics 
found  in  some  plates  it  is  cast  on  end,  and  under  a  head  of 
fluid  metal  to  ensure  its  soundness.  The  dross  rises  toward 
the  gate,  and,  as  this  is  near  the  lower  end  of  the  plate,  its 
defects  are  less  noticeable  than  when  the  method  of  pouring 
is  not  that  specified. 

"In  the  illustrations,  Figs.  30  and  31,  are  profile  views  of 
the  plates  for  which  the  construction  of  the  mold  is  adapted. 
Fig.  32  is  a  front  elevation  of  the  mold  mounted  as  for  pour- 
ing. Fig.  33  shows  a  cross-section  on  AA  in  Fig.  32,  and 
Fig.  34  is  an  end  elevation  of  the  mold,  inverted  after  cast- 
ing and  with  the  mold  opened  for  removal  of  the  cast  plate. 
Fig.  35  is  a  detailed  cross-section  of  the  slide  and  nut  of 


*  Communicated,  Mr.  W.  H.  Aldridge. 

f  United  States  Patent,  823977.     June  19,  1906. 

J  Engineering  and  Mining  Journal     May  5,  1906. 


210  LEAD  REFINING  BY  ELECTROLYSIS. 

the  opening  portion  of  the  mold,  and  Fig.  36  is  a  detail 
section  showing  a  modified  form  of  joint  between  the  head 
and  plate  portion  of  the  mold,  by  which  the  parts  which  en- 
close  the  head  are  sustained  when  inverted. 

"The  anode  plate  is  represented  by  2;  that  showrn  in  Fig. 
1  is  provided  with  laterally  projecting  horns,  3,  by  which  the 
plate  is  supported  on  the  walls  of  the  tank;  that  shown  in 
Fig.  2  has  eyes,  4,  which  are  usually  bent  and  cast  into  the 
plate,  but  may  be  cast  with  the  plate. 

"The  main  body  or  plate  portion  of  the  mold  is  formed 
of  two  recessed  parts,  5,  secured  by  any  suitable  fastening, 
so  that  the  recesses  when  together  will  leave  a  space  6,  to 
form  the  mold  of  the  lower  or  uniform  portion  of  the  plate. 
These  recesses  are  carried  to  the  end  of  the  mold,  so  that  the 
metal  may  be  poured  from  that  end  which  forms  the  lower 
part  of  the  plate  when  in  position  in  the  tank. 

"The  head  of  the  plate,  including  the  horns,  3,  or  eyes,  4, 
as  the  case  may  be,  is  formed  by  two  portions,  7,  each  hav- 
ing recesses,  8,  to  form  the  desired  width  and  shape  of  head 
which  they  entirely  enclose.  These  portions,  7,  are  slidable 
outward  from  the  middle  plane  of  the  mold  a  sufficient  dis- 
tance to  clear  the  mold  from  the  projecting  portions  of  the 
plate  which  has  been  cast  within  it.  The  contiguous  edges 
are  beveled  as  at,  8,  so  that  they  will  form  a  close  joint 
together. 

"Each  drawback  portion,  7,  is  furnished  on  each  side  with 
outwardly  projecting  members,  9,  by  which  they  are  sup- 
ported on  V-shaped  slides,  10,  on  brackets,  11.  These  project 
from  the  adjacent  sides  of  5,  and  the  parts,  7,  are  slidable  to 
or  from  the  plane  of  division  by  screws,  12,  having  right-  and 
left-hand  threads  on  their  opposite  ends.  These  pass  respect- 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     211 


(5) — «-— 15) 


FIG.  30. 


FIG.  31. 


FIG.  32. 


FIG.  33. 


17, 


FIG.  34. 


FIG.  36. 


212  LEAD  REFINING  BY  ELECTROLYSIS. 

ively  through  correponding  nuts,  13,  secured  by  screws  to 
the  parts,  7.  The  screws,  12,  are  supported  in  bearings,  14, 
upwardly  projecting  from  the  outer  ends  of  the  brackets,  11, 
and  are  rotatable  therein  by  a  hand- wheel  or  crank,  17,  on 
either  one.  A  shaft,  15,  extended  between  the  screws  and 
connected  to  them  by  beveled  pinions,  16,  enables  them  to  be 
simultaneously  operated. 

"The  mold  is  pivotally  mounted  by  trunnions,  20,  secured 
to  or  forming  a  part  of  the  plate  portion,  5,  in  a  frame,  21, 
provided  with  wheels;  it  is  furnished  with  a  hand- wheel,  22, 
Toy  which  it  may  be  inverted  in  the  frame. 

' '  In  operation  the  parts,  7,  are  tightly  closed  and  the  mold 
is  inverted  to  bring  the  open  end  of  it  uppermost  as  in  Figs. 
32  and  33.  The  metal  is  then  poured  in,  and  when  set  the 
anold  is  again  inverted,  the  parts,  7,  withdrawn,  as  represented 
In  Fig.  34,  and  the  plate  drawn  from  the  mold.  Some  draft 
may  be  desirable  in  the  width  and  thickness  of  the  plate,  to- 
Tvards  the  open  or  pouring  end  of  the  mold,  to  facilitate  its 
removal.  It  may  also  be  necessary  to  support  directly  the 
head-end  members,  7,  when  the  head  mold  is  closed,  to  enable 
them  to  sustain  their  weight  and  that  of  the  fluid  metal  within 
the  mold.  For  this  purpose  some  such  modification  as  is 
rshown  in  Fig.  36  may  be  adopted.  In  this  engaging  lips,  18, 
are  provided  on  the  contiguous  edges  of  5  and  7,  the  lips  secu- 
a-ing  these  parts  of  the  mold  against  separation  endwise. 

*' These  molds  can  be  made  with  water-jackets,  and  can 
Ibe  mounted  on  cars  in  any  number  desired,  and  can  all  be 
opened  at  once  by  the  turning  of  one  lever." 

The  molding  of  the  refined  lead  calls  for  no  special  remarks, 
Hie  usual  method  described  by  the  authorities  on  lead  smelt- 
ing being  used. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     213 

The  sampling  of  bullion  bars  received  to  be  refined,  would 
be  done  in  the  ordinary  manner,  taking  five  punches  diagonally 
across  a  row  of  five  bars  on  the  top,  and  then  turning  them 
over  on  the  bottom  and  taking  one  punch  each  from  each 
bar  in  the  same  manner,  but  on  the  opposite  diagonal.*  Sam- 
pling anodes  does  not  give  the  same  result  as  is  got  from  the 
bars  from  which  the  anodes  were  cast,  and  both  are  lower 
than  a  dip  sample  taken  from  the  lead  flowing  to  the  molds. 
I  believe  the  sample  taken  by  punching  anodes  in  a  small 
number  of  places  can  be  relied  on  very  closely,  for  usually 
in  casting  the  lead  chills  in  the  anode  mold  pretty  quickly, 
especially  in  the  lugs  and  corners,  and  you  have  a  plate  of  com- 
paratively small  and  even  thickness  to  punch  several  times 
on  both  sides.  The  following  results  in  Table  84  are  from  a 
test  made  at  Trail,  July,  1902. 

TABLE  84. 


6 
fc 

0) 

Bar 
Sample 

Dip  Sample 
Anode. 

Punch  from 
Top  Anode. 

Punch  from 
Bottom  Anode. 

Average  Top 
and  Bottom. 

•a 

I 

£ 

Au 

Ag 

Au 

Ag 

Au 

Ag 

Au 

Ag 

Au 

Ag 

i 

2.79 

322.2 

2.88 

328.6 

2.72 

316.0 

2.84 

324.7 

2.78 

320.7 

2 

2.91 

331  .  1 

2.92 

333.6 

2.90 

329.6 

2.99 

331.6 

2.94 

330.6 

Size  of  tanks. — This  will  have  to  depend  on  the  capacity 
of  the  plant.  For  fair-sized  or  large  plants  a  current  of  3500 
to  6000  amperes  is  satisfactory,  the  latter  probably  being 
more  favorable.  It  seems  evident  that  the  larger  the  tanks 
can  be  made  the  smaller  the  cost  of  tank  construction  and 


*Hofman,  "Metallurgy  of  Lead,"  1899,  page  351. 


214  LEAD  REFINING   BY   ELECTROLYSIS. 

maintenance  per  ton  produced.  The  separation  of  electrodes, 
which  is  usually  expressed  in  distance  from  center  to  center 
of  anodes,  varies  from  4f  to  411050//  as  follows: 

TABLE   85. 

Trail,  B.  C 4 . 375  inches. 

Grasselli,  Ind 4.625       " 

Newcastle-on-Tyne 4.15         " 

The  anodes  are  about  3  to  4  inches  narrower  than  the 
tanks  themselves.  The  anode  width  is  usually  about  2  feet, 
but  this  can  be  increased  as  well  as  not  to  2  feet  6  inches, 
or  even  3  feet,  and  thereby  shorten  the  tank  and  reduce 
the  number  of  electrodes  to  be  handled. 

TABLE  86. 

Plant.  Anode  Width.  Tank  Width. 

Trail,  B.  C 26  inches  30  inches 

Grasselli,  Ind 24     "  30     "      probably. 

Newcastle-on-Tyne .  .  .    33     ' '  37 

The  depth  of  the  anode  exposed  to  the  electrolyte  is  from 
2  feet  10  inches  to  3  feet. 

TABLE  87. 

Plant.  Anode  Depth. 

Trail,  B.  C 34.5  inches. 

Grasselli,  Ind 36 

Newcastle-on-Tyne 34 

Adopting  the  maximum  dimensions  now  used  in  each  case 
for  a  6000-ampere  current,  anodes  33  inches  wide  and  36  inches 
deep,  current  density  17.5  amperes  per  square  foot,  space 
center  to  center  of  anodes  4}  inches,  the  tank  would  need 
the  following  dimensions  inside:  length  8  feet,  depth  3  feet 
9  inches,  width  3  feet  1  inch. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     215 

Wood  tanks  have  been  used  exclusively,  for  which  South- 
ern yellow  pine  is  good  material.  Cedar  was  tried  at  Trail 
first  and  found  rather  soft,  and  more  recently  better  results 
have  been  obtained  with  fir. 

The  tank  of  the  future,  in  my  opinion,  will  be  made  of 
reinforced  concrete,  saturated  with  sulphur  by  immersion 
in  a  sulphur  bath.*  They  are  cheaper  than  wood  and  ab- 
solutely acid  proof.  A  small  tank  of  this  kind  in  my  labor- 
atory containing  hydrochloric  acid  is  in  the  same  condition 
after  several  months'  standing.  There  is  absolutely  no 
action  of  the  acid  on  the  tank.  Other  tanks  are  now 
being  tested  on  a  practical  scale,  with  good  results,  as  far 
as  corrosion  goes,  though  they  cracked  somewhat  in  the 
corners. 

The  preparation  of  a  concrete  tank  of  any  particular  size 
and  shape,  reinforced  or  not,  does  not  need  any  very  long 
description  here.  An  article  by  Mr.  D.  H.  Browne  |  gives 
a  good  description  of  the  manufacture  of  electrolytic  tanks, 
from  which  the  following  remarks  are  taken: 

''The  first  requisite  is  a  good,  slow-setting  cement.  Slow- 
ness of  set  is  necessary  because  in  building  large  tanks  it  re- 
quires ten  or  twelve  hours  or  even  more  to  carry  up  the  walls 
to  the  required  height,  and  as  the  ramming  must  be  contin- 
uous throughout  this  entire  time,  it  is  evident  that  if  the  bot- 
tom took  its  initial  set  before  the  sides  were  completed  it  would 
be  injured  by  the  vibration.  The  cement,  therefore,  should 
take  longer  to  set  than  the  tank  to  complete.  Cheap  cement 
is  worse  than  useless.  Saylor's  cement  has  proved  a  reliable 


*  Patent  applied  for. 

f  "  Electrochemical  and  Metallurgical  Industry,"  Vol.  I,  page  273. 


216  LEAD  REFINING  BY  ELECTROLYSIS. 

article,  but   any    brand  which  will  stand  the  'pat'  test   will 
be   satisfactory. 

"The  'pat'  test  is  made  by  mixing  a  handful  with  water 
to  a  stiff  paste  and  working  the  same  on  a  glass  plate  into 
a  cake  about  half  an  inch  high  and  3  or  4  inches  in  diameter. 
The  surface  should  be  troweled  smooth  and  the  sides  brought 
down  to  a  thin  edge.  This  is  allowed  to  stand  a  few  hours, 
then  is  covered  with  a  wet  cloth  and  set  aside  in  a  cool  place 
over  night.  If  it  sets  slowly  and  shows  no  cracks  on  the  sur- 
face or  at  the  edges  it  will  answer. 

"For  the  best  work  crushed  granite  should  be  used. 
This  has  a  rough  granular  fracture  or  'bite/  into  which  the 
sand  and  cement  lock  better  than  with  any  other  rock.  As 
the  stone  used  is  the  weakest  part,  and  as  a  good  concrete, 
when  broken,  shows  fracture  across,  and  not  around  the  par- 
ticles of  stone,  it  is  important  to  use  the  best  rock  available. 
Failing  granite  a  trap  rock  or  blue  diorite  is  a  good  substitute. 
The  size  of  the  rock  depends  on  the  thickness  of  the  walls; 
a  safe  rule  being  that  no  piece  should  be  over  one-quarter 
the  thickness  of  the  wall  in  which  it  is  used.  For  ordinary 
tanks  material  passing  through  a  screen  of  1J  inches  and  over 
a  screen  of  one  half  inch  is  satisfactory.  The  material  smaller 
than  one  half  inch  should  be  rejected,  as  it  interferes  with  the 
filling  of  the  voids. 

"The  solidity  of  concrete  depends  largely  on  the  care  with 
which  these  voids  are  filled.  To  determine  the  void  space, 
take  a  pail  of  crushed  rock,  calculate  the  volume  and  find 
the  weight.  Add  now  water  till  the  pail  is  full  and  weigh 
again.  Calculate  the  volume  of  the  water  and  simple  pro- 
portion shows  the  empty  space  between  the  particles  of  rock. 
This  space  must  be  filled  with  sand,  of  which  in  turn  the  voids 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     217 

must  be  filled  with  cement.*  The  voids  of  cement  are  in 
their  turn  filled  by  the  water  absorbed.  Hence  for  strong 
concrete  the  common  use  of  the  formula,  '4  parts  rock,  2  parts 
sand,  1  part  cement.'  For  less  careful  work  a  larger  pro- 
portion of  rock  is  often  used. 

"To  mix  the  cement  a  tight  mortar-box  or  floor  and  a 
measure  holding  one  cubic  foot  are  needed.  The  rock  should 
be  thoroughly  washed  and  the  sand  screened  from  clay  or 
gravel.  One  cubic  foot  of  cement  to  two  of  sand  is  mixed 
on  the  dry  floor  to  an  even  composition,  and  to  this  four  cu- 
bic feet  of  stone  are  added,  and  the  mass  thoroughly  shoveled 
over.  Water  is  now  added,  so  that,  while  no  muddiness  is 
apparent,  each  particle  is  moist.  The  mass  is  again  shoveled 
over  and  is  now  ready  for  the  mold. 

"This  mold  may  be  of  any  shape  whatever.  It  is  set  on 
a  solid  floor,  with  a  sheet  of  building  paper  underneath  so 
that  the  tank  does  not  bind  to  the  floor.  The  sketch  shows 
a  form  for  a  commercial-plating  bath.  The  outer  frame  is 
trued  at  right  angles  and  braced  by  struts  to  the  floor  to  pre- 
vent bulging  of  the  sides  under  the  rammer.  The  concrete 
is  now  shoveled  in,  a  few  inches  at  a  time,  and  thoroughly 
rammed  until  water  shows  at  the'  surface.  For  a  tank  of  the 
size  shown  three  men  are  needed  ramming  and  two  men  mix- 
ing and  handling  concrete.  The  tools  needed  are  iron  rammers, 
about  2  inches  thick  and  3  or  4  inches  square,  with  a  sleeve 
for  a  wooden  handle.  Such  a  tool,  handled  with  a  short, 
stiff  blow,  is  better  than  a  lighter  tool,  with  a  springy  blow, 
the  idea  being  simply  to  drive  out  the  air  from  between  the 
particles  and  completely  fill  the  voids. 

*  This  method  of  test  not  now  considered  entirely  correct. 


218  LEAD  REFINING  BY  ELECTROLYSIS. 

''As  soon  as  the  bottom  is  of  the  desired  thickness  the 
inner  frame  is  put  in  place  and  braced  by  cross-pieces  to  pre- 
vent inward  bulging.  The  sides  are  now  rammed  up,  a  few 
inches  at  a  time.  It  is  not  desirable  to  lay  the  sides  in  lay- 
ers, but  rather  to  carry  them  up  without  coursing  or  strati- 
fication. One  thing  is  very  important — that  there  be  no  stop- 
pages. If  a  mealtime  intervenes  the  men  should  be  relieved 
one  at  a  time,  so  that  no  pause  occurs  till  the  tank  is 
completed. 

"The  top  finish  is  put  on  by  bringing  the  concrete  to  within 
a  quarter  of  an  inch  from  the  top  of  the  mold  and  carry- 
ing this  up  with  equal  parts  sand  and  cement  troweled  to  a 
smooth  surface.  Any  openings  or  holes  in  the  tank  wall 
are  made  by  inserting  a  block  of  wood  of  the  desired  size  in 
the  side  walls.  After  the  tank  is  set  the  wood  can  be  drilled 
or  broken  out. 

"Three  or  four  days  should  elapse  before  the  moldboards 
are  taken  down.  The  inner  frame  is  removed  by  unscrew- 
ing the  angle  irons  shown,  when  the  side  boards  will  drop  in- 
ward without  any  difficulty.  The  outer  form  falls  apart  on 
removal  of  the  the  rods.  If  necessary  the  inner  surface  can 
be  finished  with  a  coat  of  sand  and  cement,  but  if  planed 
boards  were  used  for  the  molds  the  surface  is  usually  quite 
smooth. 

"Concrete  will  not  stand  strong  acids;  caustic  or  chlorine 
has  no  effect  upon  it.  A  coating  of  paraffine  or  tar  would 
help  it  to  resist  acids.  It  should  not  be  subjected  to  sudden 
.changes  of  temperature.  If  the  heat  be  brought  up  gradu- 
ally it  will  stand  fire.  It  can  be  handled  or  lifted  like  a  block 
of  granite  if  ordinary  care  be  used  to  prevent  the  tools  from 
bearing  against  the  sharp  edges  of  the  tank. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS-     219 

"A  tank  with  6-inch  bottom  and  4-inch  sides,  containing 
24  cubic  feet  of  concrete,  can  be  set  up  and  completed  by 
five  men  in  one  day.  The  cost  decreases  with  the  number 
of  tanks  built  at  one  time  and  the  facilities  for  handling  con- 
crete. Building  four  tanks  of  this  size  per  day  the  cost  per 
tank  was  as  follows: 

TABLE  88. 

Carpenter  and  blacksmith  labor  on  molds $1 . 75 

Concrete  work  labor,  30  hours  at  17£  cents 5.20 

3.5  cubic  feet  cement  at  60  cents 2.10 

7  cubic  feet  sand .25 

14  cubic  feet  crushed  trap  rock 3 . 00 


$12.30 

"Including  finishing,  taking  down  molds,  cementing  in 
rubber-pipe  connections,  about  $15  will  cover  the  cost  of 
building  a  tank  as  above  described,  the  dimensions  of 
which  are  about  3  feet  wide,  9  feet  long  and  2  feet  deep. 
No  construction  of  lead,  slate  or  wood  can  be  made 
which  will  fulfill  all  the  requirements  of  the  case  for  this 


sum." 


To  make  the  tank  acid-proof,  after  standing  moist  for 
several  weeks  until  well  set,  the  tank  is  dried  out  pretty  well, 
and  then  lowered  into  an  iron  vessel  containing  just-melted 
sulphur.  The  sulphur  is  gradually  heated  to  150°  C.  or  so, 
but  not  to  the  thickening  point.  This  should  take  quite  a 
number  of  hours,  perhaps  12,  steam  coming  off  regularly  as 
long  as  the  temperature  is  rising,  and  of  course  removing 
with  it  all  permanent  gases  present  in  the  concrete.  The 
sulphur  is  then  allowed  to  cool  slowly  during  another  6  to  12 
hours,  when  the  sulphur  penetrates  the  crevices  and  cracks 
in  the  concrete.  Probably  the  atmospheric  pressure  helps 


220  LEAD  REFINING  BY  ELECTROLYSIS. 

in  this,  as  the  reabsorption  and  contraction  of  steam  in  cooling 
would  make  a  vacuum  in  the  concrete. 

The  tank  is  then  lifted  out,  and  after  cooling  to  perhaps 
80°  to  90°  C.,  is  quickly  dipped  in  again  and  taken  out.  This 
chills  a  thin,  smooth  layer  of  sulphur  on  the  tank,  and  fills 
any  cracks,  while  the  coating  produced  does  not  come  off  or 
crack  off  during  long  periods.  A  coating  of  asphaltum  paint 
applied  later  is  partially  absorbed  by  the  spaces  between  the 
sulphur  crystals  and  adheres  very  well.  In  fact  the  surface 
of  the  finished  tank  will  soak  up  quite  a  little  paint,  melted 
paraffine,  etc. 

Wooden  tanks  have  been  built  with  all  bolts  clear  of  the 
wood  and  with  bolts  through  the  wood.  Figs.  37  and  38  show 
the  two  methods  of  construction.  The  bolts  in  the  wood 
show  corrosion  badly  sometimes,  especially  where  the  bolts 
pass  from  one  plank  to  another.  Iron  is  not  rapidly  attacked 
by  the  lead-depositing  electrolyte  when  no  current  is  passing 
in  the  neighborhood,  but  as  there  are  slight  differences  of 
e.m.f.  between  different  parts  of  the  tank,  it  would  only  be 
expected  that  lead  would  deposit  on  one  part  of  an  iron 
conductor  touching  the  solution  at  several  places,  and  iron 
dissolve  at  another.  For  this  reason  bolts  clear  of  the  wood 
could  be  expected  to  last  longest.  The  first  tanks  at  Trail  were 
made  in  this  way,  but  in  the  tanks  used  now  the  bolts  pass 
directly  through  the  wood.  If  the  bolts  could  be  surrounded 
by  a  rubber  tube,  or  copper  bolts  used,  they  would  then  be 
most  successful.  The  expedient  of  pouring  hot  paraffine, 
pitch,  etc.,  through  the  holes  before  putting  in  the  bolts,  seems 
to  help  a  little,  but  not  to  be  entirely  successful.  In  design- 
ing a  wooden  tank,  the  placing  of  the  bolts  should  be  studied 
not  only  from  the  mechanical  standpoint,  but  to  reduce  elec- 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS-     221 

trolytic   corrosion  of  the  iron  as  far  as  possible,  which  I  am 
satisfied  is  the  main  cause  of  the  failure  of  the  bolts. 

As  an  example,  if  two  tanks  are  bolted  together,  as  shown 
in  Fig.  39,  it  is  evident  that  the  current  will  tend  to   pass 


((oj) 


\t 


FIG.  37. 


through  the  wet  wood  to  the  iron  bolt  in  one  tank,  depositing 
lead  on  it  probably,  and  pass  from  the  bolt  to  the  solution 
in  the  other  tank,  with  too  rapid  corrosion  of  the  bolt.  It 
would  be  expected  that  the  greatest  effect  on  the  bolt  would 


222 


LEAD   REFINING   BY   ELECTROLYSIS. 


o   % 


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FIG.  38. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     223 

be  where  it  passes  from  one  plank  to  another,  unless  the  joint 
in  the  wood  were  perfect.  As  a  matter  of  fact,  that  is  where 
bolts  fail  usually.  Bolts  as  shown  in  Figs.  40  and  41  would 
be  apt  to  carry  current  as  shown,  if  the  tanks  rested  on  a  wet 
beam. 

A  few  tenths  of  an  ampere  would  cut  a  bolt  through  in  a 
moderate  time. 

Three-  or  four-inch  planking  should  be  used  for  tank  walls 
and  bottom,  four  inches  being  best.  Tanks  with  four-inch 
sides  do  not  need  a  bolt  across  the  top  in  the  center  or  braces 
to  hold  the  sides  from  bulging.  The  use  of  feather  and  groove 
in  the  joints  is  preferred  by  some  and  not  by  others. 

The  problems  to  be  settled  in  connection  with  the  tanks  are 
their  arrangement  and  differences  of  elevation  for  circula- 
tion purposes.  Two  general  systems  of  locating  tanks  for 
the  multiple  system  are  in  use  both  in  electrolytic  copper  and 
lead  refining.  The  older  method,  which  we  may  call  the 
"cascade,"  originated,  I  believe,  by  Mr.  F.  A.  Thum,  uses 
double  rows  of  tanks  end  to  end,  each  pair  at  an  elevation 
of  2J-3  inches  above  the  next  pair,  while  a  continuous  cir- 
culation of  solution  flows  from  the  highest  tank  at  one  end 
to  the  lowest  at  the  other.  The  newer  arrangement  pat- 
ented by  Mr.  A.  L.  Walker  *  offers  some  important  advantages 
especially  for  copper  refineries,  in  requiring  less  space,  less 
copper  conductors  by  far,  and  saving  some  power.  For  lead 
refining,  considering  that  the  number  of  tanks,  amount  of 
conductors  and  power  are  only  about  a  third  as  great  per  ton 
produced  as  in  copper  refining,  it  is  evident  that  these  advan- 
tages are  much  reduced  when  the  Walker  arrangement  is  ap- 

*  U.  S.  Patent  687800.     December  3,  1901. 


224 


LEAD  REFINING  BY  ELECTROLYSIS, 


K 

1  t.l 

-h 

Tin 

1    1    1 

1  1  t 

If 

-  -  - 

FIG.  39. 


4 

LLU 

Tit! 

rd 

V. 

a 

p 

I 

js 

y 

/ 

FIG.  40. 


f 


a 


FIG.  41, 


S. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     227 

plied  to  lead,  while  the  disadvantages,  which  are  of  a  mechan- 
ical nature  due  to  greater  crowding,  are  increased  somewhat. 
There  is  also  more  chance  for  injury  to  the  workmen  with  the 
Walker  system. 

The  first  tanks  at  Trail,  shown  in  Plate  7,  were  arranged 
by  the  cascade  system.  The  next  tanks  had  the  newer  ar- 
rangement, and  the  two  systems  were  operated  side  by  side, 
the  old  arrangement  giving  much  higher  efficiency  and  better 
satisfaction.  As  thereafter  more  tanks  were  added  according 
to  the  old  system,  it  is  to  be  inferred  that  the  old  system 
was  considered  best.  The  Grasselli  plant  of  the  United  States 
Metals  Refining  Company  uses  the  Walker  system. 

The  Walker  system  uses  less  power  and  less  copper  bus 
bars,  which  latter  may  be  taken  to  be  about  $50  less  per  ton 
per  day  installed  in  first  cost  of  copper.  The  saving  in  space 
would  not  amount  to  over  about  80  sq.  ft.  of  area  per  ton  of 
lead  per  day,  as  the  tanks  are  usually  installed;  worth  say 
$80  per  tori  refined  per  day.  The  power  lost  in  the  bus  bars 
from  tank  to  tank  with  the  old  system,  using  5  sq.  in.  of 
copper  for  4000  amperes,  is  about  85  watts  per  tank,  or  per 
ton  per  day,  about  235  watt  days  =  5. 6  K.W.  hours  per  ton 
lead,  or  4.3  cents'  worth,  with  power  at  $50  per  year.  A  loss 
of  current  efficiency  of  6%  (which  may  be  expected  when 
leaking  wooden  tanks  are  placed  in  two  continuous  rows  close 
together)  would  offset  this  gain.  With  absolutely  tight  and 
non-conducting  concrete  tanks  mentioned  on  page  23,  there 
would  be  however  no  objection  from  current  leaks.  The  only 
saving  by  the  Walker  system  is  then  about  $130  per  ton  per 
day  in  first  cost,  and  4  cents  per  ton  in  power,  a  total  of  about 
8  cents  per  ton,  figuring  interest  on  cost  for  extra  copper  and 
extra  space  as  high  as  10%. 


228  LEAD  REFINING  BY   ELECTROLYSIS. 

Subdivision  of  tanks  into  blocks. — With  the  cascade  sys- 
tem we  can  have  a  sloping  floor  so  that  the  tanks  are  every- 
where at  the  same  height  above  the  floor,  which  is  however 
not  as  good  as  a  level  floor  with  tanks  at  various  elevations 
above  the  floor.  Allowing  2J  inches  drop  between  the  tanks 
end  to  end,  probably  not  more  than  7  or  8  tanks  can  be  used 
for  each  circulation  system,  making  blocks  of  14-16  tanks, 
occupying  a  space  of  6  to  7  feet  by  50  to  65  feet.  With  the 
Walker  system  any  number  of  tanks  may  be  placed  side  by 
side  in  one  row,  the  circulation  being  from  row  to  row,  which 
are  at  different  levels,  and  not  from  tank  to  tank.  Four  rows 
are  usually  arranged  in  a  bay  50  to  55  feet  wide. 

Cathodes. — The  first  cathodes*  used  were  of  lead-plated 
sheet-iron.  In  the  use  of  these  cathodes  it  was  noticed  that  a 
preliminary  plating  of  copper  prevented  corrosion  of  the  iron 
underneath.  At  Trail  a  number  of  tanks  were  operated  for 
some  months  with  ene-eighth  inch  sheet  steel  cathodes,  but 
the  experiment  was  not  regarded  as  successful.  The  cathodes 
were  provided  with  grooved  wooden  strips  which  fitted  on 
their  edges,  to  prevent  the  growth  of  lead  where  it  could  in- 
terfere with  pulling  the  deposits  off.  The  lack  of  success 
was  on  account  of  lack  of  sufficient  care  in  the  preparation 
and  plating  of  the  sheets.  Some  of  the  cathodes  which  were 
carefully  plated  for  depositing  starting  sheets  were  not  at- 
tacked, but  most  of  the  others  were.  When  not  well  pro- 
tected by  copper  and  lead  the  iron  pitted,  and  the  deposited 
lead  was  not  as  hard  and  solid  as  when  deposited  on  lead. 

On  the  other  hand  the  labor  was  much  less  with  the  steel 
cathodes,  and  there  were  no  short  circuits  from  the  anodes 

*U.  S.   Patent,   A.   (J.   Betts,   679824.      August  6,    1901. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     229 

and  cathodes  touching.  Had  they  been  carefully  plated  with 
copper  before  lead-plating  them,  and  replated  if  worn  out, 
their  use  would  probably  not  have  been  abandoned.  The 
cost  for  plant  is  of  course  greater  with  steel  cathodes, 
namely  about  $100  per  ton  refined  per  day.  .  Those  used  at 
Trail  were  made  of  tank  steel  and  had  to  be  selected,  as 
some  of  the  steel  was  too  much  warped.  By  stretching, 
perfectly  flat  sheets  could  be  produced,  and  this  is  an  actual 
manufactured  article  I  am  told,  though  I  have  not  been  able 
to  find  out  where  stretched  steel  sheets  are  made.  A  copper 
bolt  was  riveted  and  soldered  to  the  cathode  lug  to  take 
the  current,  while  the  upper  part  of  the  steel  cathode  was 
painted  with  P.  &  B.  paint  as  a  protection  from  acid  spatter- 
ing on  them.  They  were  greased  before  receiving  the  deposit 
so  that  it  could  be  readily  removed.  These  cathodes  may 
be  seen  in  Plate  7.  The  two  round  holes  were  used  for 
lifting. 

Usually  lead  cathodes  are  used,  either  of  deposited  or  cast 
sheets.  The  first  cathodes  used  at  Trail  were  of  deposited 
lead,  made  in  four  tanks  six  inches  deeper  than  the  others, 
with  correspondingly  longer  anodes  and  cathodes,  the  latter 
of  copper-  and  lead-plated  steel.  These  cathodes  had  been 
carefully  prepared,  and  very  good  deposits  of  lead  were  ob- 
tained, which  were  stripped  off  and  wrapped  by  hand  around 
the  copper  cross-bars  for  the  other  twenty-four  tanks.  For 
greasing  the  steel  cathodes  a  solution  of  paraffine  dissolved 
in  benzine  was  used.  It  was  found  necessary  to  let  the  ben- 
zine dry  off '  or  otherwise  the  deposited  lead  stuck  fast. 

The  rough  side  of  the  sheet  was  put  next  the  cross-bar 
to  give  better  contact,  but  the  contacts  were  not  as  good  as 
could  be  wished.  At  one  time  clips  were  put  on  the  cathode 


230 


LEAD  REFINING  BY  ELECTROLYSIS. 


bars  to  try  to  improve  the  contact,   but  this  was  not  worth 
the  trouble.     The  clips  may  be  seen  in  Plate  7. 

A  great  many  plans  were  suggested  for  casting  thin  cathode 


— -}  — 


-6-4H 


fM?n 


FIG.  42. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     231 

sheets,  including  rolling,  dipping  cold  iron  plates  into  melted 
lead,  revolving  a  cooled  steel  drum  in  a  lead  pot,  and  rolling 
up  the  resulting  lead  strip  to  be  afterwards  cut  into  lengths. 
Mr.  John  F.  Miller,  of  the  Canadian  Smelting  Works,  brought 
out  the  apparatus  used  at  present.  Pure  lead  is  kept  just 
melted  in  a  small  pot  and  ladled  into  a  pivoted  trough  at  the 
upper  end  of  a  sloping  iron  plate  (see  Fig.  42).  The  lead  in 
the  trough  is  then  tipped  on  the  plate,  where  most  of  it  solidi- 


FIG.  54. 

fies  in  a  thin  even  plate,  while  some  is  thrown  off  at  the  bot- 
tom. These  sheets  are  then  thrown  on  a  pile,  and  later  on 
wrapped  around  the  cathode  cross-bars  by  hand. 

Dr.  Wm.  Valentine  has  improved  this  cathode  by  casting 
two  lugs  on  at  the  bottom  of  the  plate  at  the  same  time  the 
plate  itself  is  cast,  using  suitable  molds  in  connection  with 
the  plate.  His  cathode  is  illustrated  in  Fig.  43.  The  cathode 
rod,  which  is  round  except  where  flattened  at  one  end  for  con- 
tact with  the  bus  bar,  is  inserted  in  the  holes  in  the  lugs.  Fig. 
44  explains  the  operation  of  the  apparatus  used. 


232 


LEAD  REFINING  BY  ELECTYOLYSIS. 


This  gives  a  suspension 
from  the  center  of  the  cathode 
bar,  while  by  the  old  method 
the  lead  is  suspended  from  one 
side,  and  the  rod  has  to  be 
kept  from  turning  when  rest- 
ing on  the  tank  and  being  car- 
ried by  the  crane,  by  giving 


FIG.  44. 

the  rod  a  special  shape,  and 
using  a  special  hook  on  the 
crane  (see  Fig.  45).  The  con- 
tact with  the  Valentine  cathode 
is  almost  perfect,  which  is  a 
further  advantage. 

The  lead  cathodes  are  all 
too  flimsy  and  require  straight- 
ening before  use,  and  careful 
handling  to  the  tanks,  and  then 
there  are  sure  to  be  short  cir- 
cuits. In  tanks  where  no  short 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     233 

circuit  actually  exists,  the  uneven  spacing  of  the  electrodes 
causes  the  anodes  to  dissolve  unevenly,  which  is  a  bad  thing 
for  a  number  of  reasons.  Methods  that  will  insure  an  even 
spacing  of  electrodes  and  uniform  contacts  are  worth  stri- 
ving for  in  electrolytic  refining. 

Cathode  bars. — These  are  usually  of  copper.  At  Trail 
rods  J  inchxl  inch  on  edge  were  found  strong  enough.  •  The 
two  ends  were  twisted  flat  and  offset  one  half  inch  at  the  same 
time,  as  shown  in  the  sketch,  to  prevent  the  cathode  sheet 
from  turning  the  rod.  See  Fig.  46.  These  rods  weighed  about 


FIG.  46. 

6  Ibs.  each.  As  J  sq.  in.  of  copper  is  more  than  necessary  to 
carry  200  amperes,  and  copper  is  so  much  softer  than  steel, 
a  combination  rod  is  cheaper  and  better.  Steel  tubing  plated 
with  copper  about  iV-inch  thick  is  also  in  use.  The  plating 
can  be  readily  done  by  any  electro-chemist  or  plater  of  ordinary 
skill. 

Tank  foundations,  supports,  and  arrangement  to  catch  leaks. 
— Brick  piers  of  sectional  area  corresponding  to  their  height, 
with  a  concrete  base,  and  glass  plate  half  inch  thick  on  top 
for  insulation,  make  good  supports.  Concrete  is  also  good. 
A  good  way  of  placing  the  tanks  relative  to  the  piers,  for 
the  cascade  arrangement  of  tanks,  is  not  to  have  the  piers 
under  the  tanks,  but  under  the  aisles  between  the  tanks,  while 
the  tanks  are  carried  on  heavy  cross-beams.  See  Fig.  47. 
By  cutting  a  small  notch  from  the  beams  near  the  piers,  any 
acid  solution  is  prevented  from  running  down  the  piers  into 
the  ground.  It  is  more  difficult  to  collect  any  leaks  on  a 


234 


LEAD  REFINING  BY  ELECTROLYSIS. 


vertical   support   than  that  which  drops  free  on  the  sloping 
boards  underneath. 

Cleaning  tanks. — The  usual  plan  in  a  copper  refinery  is 
to  have  apparatus  arranged  so  that  the  slime  can  be  sluiced 
out  of  the  tank.  In  a  lead  refinery  the  conditions  are  different, 


FIG.  47. 

for  the  lead  slime  is  denser  and  heavier,  and  generally  only  a 
small  proportion  drops  from  the  anode  anyway,  and  it  is  often 
removed  in  a  separate  cleaning  tank.  At  Trail  we  tried  the 
plan  of  sluicing  slime  into  a  tank  car  in  the  cellar,  but  the  appa- 
ratus was  not  well  arranged,  and  the  slime  was  too  thick  to 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     235 

run  out.  For  this  method  of  removing  slime,  which  has  a  gcod 
deal  to  recommend  it,  a  tank  with  hopper-shaped  bottom 
ought  to  be  used.  This  is  difficult  to  make  of  wood,  but  there 
would  be  no  difficulty  in  making  a  concrete  tank  with  such 
a  bottom.  See  Figs.  47  and  48. 

The  usual  method  of  emptying  a  tank  is  to  take  out  the 
cathodes  first  and  then  the    anodes.      The  clear  solution  is 


~i  4"  V 


FIG.  48. 

next  siphoned  off  into  the  launder  leading  to  the  low-level 
storage  tanks,  and  the  slime  shoveled  into  a  barrel,  while  the 
tank  may  next  be  cleaned  with  a  sponge. 

On  the  method  of  cleaning  tanks  adopted  depends  the 
height  of  the  cellar.  In  one  case  there  must  be  head  room 
in  the  cellar,  the  expedient  of  sluicing  the  slime  all  the  way 
to  a  common  collecting  point  requiring  too  steep  a  pitch,  so 
tank  cars  must  be  used  which  can  be  run  under  any  tank. 
This  means  a  more  expensive  plant  for  excavation  and  pillars, 
but  it  has  the  advantage  of  diminishing  labor  cost,  and  the 
tanks  can  be  washed  absolutely  clean.  When  electrolyte  is 
added  to  a  dirty  tank  the  slime  present  is  stirred  up  and  set- 


236  LEAD  REFINING  BY  ELECTROLYSIS. 

ties  slowly,  and  a  good  proportion  may  be  expected  to  settle 
on  the  cathodes.  The  sluicing  method  will  give  therefore 
the  best  results,  and  the  extra  first  cost  is  not  very  great.  For 
relatively  impure  lead,  containing  say  2%  of  antimony  and 
arsenic,  the  slime  remains  so  firmly  attached  to  the  anodes 
that  little  or  no  slime  falls  into  the  tanks  anyway,  and  in  this 
case  the  simplest  plant  will  be  equally  as  easy  to  operate,  on 
account  of  much  less  frequent  cleaning  being  necessary. 

An  arrangement  with  track  underneath  for  carrying  slime 
out  is  shown  in  Fig.  47.  The  only  sure  way  of  getting  the 
slime  to  run  is  to  have  it  drop  directly,  so  the  tank  car  should 
be  run  directly  underneath  the  tanks. 

Floors  of  a  mixture  of  asphalt  and  barite  are  used  and  are 
expected  to  be  solution-tight,  but  it  is  doubtful  if  an  entirely 
solution-tight  floor  can  be  made  in  this  way.  There  are  never- 
theless some  excellent  and  cheap  materials  available  for  catch- 
ing the  leaks.  Ordinary  tarred  roofing  paper,  supported  on 
boards,  is  good,  and  so  is  roofing  paper  that  has  been  soaked 
in  paraffine.  The  solution  has  no  effect  whatever  on  the  latter. 
The  experiment  has  not  been  tried,  but  I  feel  sure  it  would 
be  successful  to  cut  building  paper  into  squares,  soak  them 
in  paraffine,  and  lay  the  squares  like  shingles  on  a  nicely  pre- 
pared sloping  surface,  either  of  the  ground  itself,  or  the  same 
lightly  cemented. 

The  slime-car  arrangement  adds  to  the  construction  cost, 
as  can  be  readily  seen,  for  extra  height  and  weight  of  pillars, 
excavation  and  tracks,  by  an  amount  which  would  probably 
be  about  $45  per  ton  per  day.  Nothing  is  included  in  this 
estimate  for  tank  car  and  haulage  apparatus,  as  this  substi- 
tutes for  other  apparatus  in  the  other  plan.  Capitalized  at 
10%  this  would  be  1.3  cents  per  ton,  while  the  labor  and 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS-     237 

time  saved,  beside  making  better  lead,  would  be  several  times 
that  much. 

Contacts. — The  plain  copper  to  copper  surface  has  been 
tried  and  found  best.  Other  methods  have  been  tried  and 
given  up.  Mercury  contacts  are  not  good.  The  mercury 
disappears  rapidly  and  is  probably  absorbed  by  the  copper. 
If  the  copper  contacts  are  sand-papered  off,  the  drop  in  e.m.f. 
will  average  about  0.01  volt  copper  to  copper,  or  copper  to 
lead  anode.  For  the  anodes,  letting  the  anode  lug  rest  di- 
rectly on  the  copper  bus  bar,  gives  a  very  good  contact.  The 
under  side  of  the  anode  lug  must  be  cast  flat  in  order  that 
the  anode  shall  hang  straight,  and  this  at  the  same  time  makes 
it  certain  that  it  will  hang  straight. 

Circulation  of  electrolyte. — A  heavier  solution  contin- 
ually falls  from  the  anodes  when  in  action,  while  a  lighter 


FIG.  49. 

solution  rises  at  the  cathodes.  Depositing  35  Ibs.  of  lead 
per  hour  in  a  tank  causes  quick  decomposition  into  a  heavy 
layer  on  the  bottom  and  a  light  one  on  top.  If  the  current 
is  shut  off,  and  the  anodes  have  a  layer  of  slime  attached, 
heavy  solution  diffuses  from  the  slime  for  some  time  after- 
ward. The  general  method  of  circulation  from  tank  to  tank 
with  the  cascade  arrangement  is  illustrated  in  Fig.  49.  Rubber 
hose  1J  inch  internal  diameter  is  fitted  in  the  overflow  end  of 


'238  LEAD  REFINING  BY  ELECTROLYSIS. 

-one  tank  and  rests  in  a  notch  at  the  inflow  end  of  the  other 
An  apron  of  three-quarter  inch  wood  with  a  half-inch  to  one 

-inch  space  between  it  and  the  end  of  the  tank,  insures  that 
only  the  heavy  solution  at  the  bottom  of  the  tank  can  overflow 

•  to'  the  top  of  the  next.     Some  trouble  has  been  experienced 
by  the  wooden  apron  shrinking  and  opening  its  seams  so  that 
lighter  solution  can    run  through.     The    use  of    hard-rubber 
tubes  has  been  attempted  in  place  of  the  aprons,  but  I  do  not 
'know  whether  it  is  so  successful  in  preventing  the  agitation  or 
Suction  of  slime.     My  idea  in  using  the  aprons  originally  was 

•to  have  a  very  slow  motion  of  electrolyte  at  any  one  place. 

-  A  hard-rubber  tube  takes  up  as  much  distance  from  the  end 
of  the  tank  as  the  apron,  and  the  objection  to  cracks  open- 

.  ing  in  the'  apron  does  not  amount  to  much,  for  they  can  be 

-easily  calked  up  when  the  tank  is  emptied. 

Certain  precautions  are  necessary  to  keep  the  tanks  from 
overflowing  on  account  of  the  heavier  solution  at  the  bottom. 
If  the  circulation  is  uninterrupted  the  difference  in  level  on 
the  two  sides  of  the  apron  will  not  be  much  more  than  half 
an  inch.  If  the  circulation  is  cut  off,  even  when  the  current 
has  been  just  cut  off  too,  a  sufficiently  heavier  layer  may  after- 
ward collect  (from  the  diffusion  of  the  heavy  solution  in  the 
anode  slime)  sufficient  to  cause  the  tanks  to  overflow  when 

r  circulation  is  again  started,  instead  of  forcing  the  heavy  solu- 
tion behind  the  apron  out  at  the  end.     It  is  very  inconven- 

•  lent  to  have  the  solution  refuse  to  pass  from  tank  to  tank, 
"and  about  the  only  thing  to  do  is  to  take  out  some  electrodes 

..  in  each  tank,  or  move  them  to  one  end,  and  stir  the  tank  with 
'a  stick.    It  is  also  possible  to  siphon  off  some  of  the  heavy 

-  solution  at  the  bottom  and  let  the  tank  fill  with  fresh  solu- 

,  •  In  actual  refining  the  overflowing  of   the   tanks   is   a 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     239 

rare  occurrence,  but  the  causes  should  be  kept  in  mind  so  that 
it  will  be  rare. 

The  volume  of  solution  passed  through  a  4000  ampere 
tank  can  not  be  so  small  as  to  allow  of  the  production  of  much 
variation  in  density  between  top  and  bottom  of  the  tank, 
nor  too  great  to  prevent  the  slime  from  settling.  Five  gal- 
lons per  minute  is  a  fair  amount.  The  difference  in  density 
between  the  top  and  bottom  is  about  3%,  and  sometimes 
about  5%  in  practice. 

Several  kinds  of  pumps  have  been  in  use,  giving  varying 
satisfaction.     Hard-rubber    and     bronze     centrifugal     pumps, 
driven  by  small  electric  motors  and  connected  in  the  circula- 
tion system  by  good  rubber  hose,  are  in  use  and  are  very  good. 
Hard-ruuuer    plunger-pumps    are    also  satisfactory.     Air  lifts 
using    two    automatically    operated    montejus,    as    described 
in  various  books,  were  tried  at  Trail  first,  and  found  to  be 
very   poor   for   the   purpose.     A   wooden    plunger-pump    was 
then  hastily  constructed  and  installed  and  lasted  for  a  con- 
siderable  period   with  occasional   repairs.     The   pump   was   a 
long  square  box  of  2-inch  planks  about  5  or  6  inches  inside, 
with  a  square  wood  plunger,  and  leather  flaps.     Solid  rubber 
balls  about  2J-inch  diameter,  on  a  1J-  to  If -inch  hole,  made 
excellent  valves.     Iron  was  used  in  the  construction  of  the 
pump,  and  even  in  the  solution  itself  it  lasted  a  long  time. 
Copper  may  be  used  in  the  construction  of  the  pumps, 
especially  when  in  contact  with  lead,  so  a  modification  of  the 
wood   plunger-pump,  using  a  copper  tube  with  lead  plunger 
and  lead  valve  at  the  bottom,  would  be  sure  to  make  a  good 
pump.     Fig.  50.     A  plunger-pump  has  the  advantage  of  not 
churning  any  air  in  with  the  solution,  and  can  be  expected 
to  make  somewhat  purer  lead.     It  is  difficult  to  see  how  dis- 


240 


LEAD  REFINING  BY  ELECTROLYSIS. 


FIG.  50. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     241 

solved  oxygen  in  the  electrolyte  could  fail  to  oxidize  some 
slime,  thereby  dissolving  a  little  antimony  which  would  partly 
go  into  the  cathodes. 

The  deposition  of  the  overflow  tanks  and  pumps  may  be 
varied,  some  methods  being  shown  in  Figs.  51  and  52.  For 
filling  tanks  after  cleaning  out,  the  arrangement  with  a  stor- 
age tank  at  a  higher  level  from  which  tanks  that  have  been 
emptied  may  be  quickly  filled,  has  some  advantages,  and  is 


FIG.  51. 


FIG.  52. 

probably  the  best.  The  other  way  of  letting  tanks  fill  by 
putting  them  in  the  circulation  system  again,  requiring  an 
hour  or  two  to  fill  a  tank,  while  all  below  in  the  same  series 
are  without  circulation,  is  not  to  be  recommended. 

Considerable  storage  should  be  provided  for  electrolyte 
from  tanks  which  may  be  emptied  for  cleaning.  It  is  con- 
venient with  the  cascade  arrangement  to  cut  out  two  or  four 
tanks  at  once;  and  to  provide  for  two  sets  of  four  tanks  out, 
with  two  to  spare,  or  a  storage  of  say  800  cu.  ft.,  will  not  be 
found  excessive.  Two  tanks  of  400  cu.  ft.  each,  so  that  one 


242  LEAD  REFINING  BY  ELECTROLYSIS. 

can  be  removed  or  repaired,  would  be  good  practice  for  wood 
tanks,  and  a  considerably  larger  number  of  sulphur-treated 
concrete  tanks  of  the  same  size  as  the  electrolytic  tanks  would 
be  right  for  concrete  tanks.  These  latter  could  be  made  ab- 
solutely tight,  and  could  be  connected  together  by  siphons 
as  far  as  desired,  so  as  to  reduce  the  number  of  units  to  be 
considered  to  one,  with  the  possibility  of  always  cutting  out 
any  desired  tank  for  repairs. 

These  storage  tanks  are  placed  at  so  low  a  level  that  all 
liquids  from  the  lead  tanks,  whether  by  leaks  or  siphons,  run 
to  them  by  gravity. 

There  is  also  to  be  provided  another  set  of  350  cubic  feet 
capacity  at  a  level  above  all  the  tanks  so  that  it  may  be  dis- 
tributed by  hose  to  any  part,  with  a  pump  to  raise  solution 
from  the  low-level  storage  set  to  the  high  storage  tank. 

Electrolyte. — The  composition  of  the  electrolyte  is  treated 
in  Chapters  I  and  V.  The  quantity  required,  with  anodes 
spaced  4f  inches  center  to  center,  current  density  15  amperes 
per  sq.  ft.,  is  about  120  cu.  ft.  per  ton  deposited  per  day.  If 
this  contains  200  gr.  SiF6  and  80  gr.  lead  per  litre,  its  cost  is 
about  $1.25  per  cu.  ft.  as  follows: 

TABLE  89. 

25.7  Ibs.  fluorspar  at  $14  per  ton $0. 180 

34.7  Ibs.  66°  H-SO,  at  $12  per  ton 0.208 

29  Ibs.  fine  quartz  at  $10  per  ton 0 . 145 

Coal,  15  Ibs 0 .020 

Labor 0.220 

Repairs 0. 100 

6  Ibs.  white  lead  at  6£  cents  per  pound 0 . 375 

$1.248 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     243 

The  yield  on  fluorspar  and  sulphuric  acid  taken  is  as- 
sumed to  be  only  80%  and  92%  respectively.  The  item  for 
repairs  is  quite  large,  as  lead  storage  tanks  and  condensers 
do  not  last  very  well.  The  cost  of  the  acid  itself  without  the 
white  lead  is  $0.87  per  cubic  foot  of  electrolyte,  or  7  cents 
per  Ib.  anhydrous  H2SiF6,  the  latter  item  being  of  interest 
because  H2SiF6  only  is  needed  for  renewals  to  keep  up  the 
strength  of  the  electrolyte.  Electrolyte  with  160  gr.  SiF6 
and  64  gr.  Pb  would  cost  about  $1.00  per  cu.  ft. 

By  dissolving  lead  in  the  solution  electrolytically,  instead 
of  using  white  lead,  the  cost  of  electrolyte  could  be  reduced 


PIG.  53. 

by  perhaps  10-15  cents  per  cu.  ft.  A  very  simple  arrange- 
ment of  tanks  is  required,  and  the  power  necessary  is  small, 
namely,  about  25-ampere  days  per  cubic  foot.  For  a  100 
ton  per  day  refinery  the  hydrofluoric  acid  would  be  made 
slowly,  requiring  say  two  months  or  more.  The  power  for 
dissolving  the  lead  electrolytically  could  be  supplied  for  ex- 
ample by  a  12-volt  500-ampere  generator,  operating  10  cells 
in  series,  putting  the  necessary  lead  into  solution  as  fast  as 
the  acid  was  made.  See  Fig.  53.  Current  densities  of  50 
amperes  per  sq.  ft.  would  be  allowable,  and  the  cells  would 


244  LEAD  REFINING  BY  ELECTROLYSIS. 

then  be  only  about  4  ft.  square  over  all.  A  purer  electro- 
lyte to  start  with  may  be  produced  at  less  cost  in  this  way, 
and  it  is  therefore  to  be  recommended. 

Washing  appliances  for  electrodes.— It  has  been  the  cus- 
tom to  inspect  each  finished  cathode  separately  to  get  off  any 
patches  of  slime,  but  these  patches  come  from  bad  work  or 
crudely  cast  anodes  and  flimsy  cathodes  touching  the  anodes. 
This,  while  excusable  in  early  work,  is  no  longer  necessary, 
so  that  the  inspection  of  individual  cathodes  and  brushing 
where  slime  is  attached  is  no  longer  necessary  when  washing. 
The  copper  refiners  spray  a  whole  tank-load  of  cathodes  at 
once  with  hot  water  from  a  set  of  perforated  pipes,  between 
which  the  crane  lowers  and  raises  a  tank-load  of  plates.  Lead 
can  of  course  be  washed  the  same  way.  Dipping  cathodes 
into  a  tank  of  wash-water  does  not  give  so  complete  a  wash 
with  a  given  quantity  of  water  and  is  more  troublesome. 

Anode  scrap  may  be  cleaned  before  removing  it  from 
the  refining-tank,  by  standing  over  the  tank  and  passing  a 
wiper  over  the  surface  of  each  plate  to  loosen  the  slime,  pro- 
vided the  slime  is  uniform  and  not  too  hard.  With  drossy 
anodes,  hard  spots  are  found  in  the  slime  that  do  not  come 
off  very  easily,  and  such  anodes  have  been  wiped  by  hand 
in  special  cleaning-tanks.  For  slime  which  remains  attached 
securely  enough  to  stand  removing  with  the  anode  scrap  (as 
is  usually  the  case)  wiping  apparatus,  such  as  shown  in  Fig. 
54,  is  recommended.  This  would  not  work  with  slime  from 
very  hard  lead,  say  3-10%  Sb,  as  this  has  to  be  scraped 
off. 

Regarding  the  presence  of  hard  particles  of  slime,  this 
results  on  one  side  of  the  anode  only  where  the  dross  collects 
during  cooling.  This  is  obviated  by  the  use  of  closed  molds, 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     245 


and   also  by  casting  the  lead  anodes  from  the  melting-pot  at 
a  low  temperature,  leaving  the  dross  undisturbed  on  the  sur- 


1  ,f 


SI 


!    x 


/     /         ux    /         ",' 

^I^Ll^^l^L~"^L^^I~^lI^ 


It 


FIG.  54. 


face  until  most  of  the  lead  has  been  cast,  and  then  raising 
the  heat  enough  to  soften  the  dross  so  that  it  may  be  dipped 


246  LEAD  REFINING  BY  ELECTROLYSIS. 

into  a  separate  lot  of  anodes,  to  be  refined  in  a  few  special 
tanks  and  afterward  cleaned  of  slime  by  themselves. 

After  removing  the  slime  the  anode  scrap  is  sprayed,  dried 
and  melted,  while  the  wash- water  is  used  in  washing  slime. 
The  wash-water  from  the  cathodes  is  sometimes  used  over 
and  over  until  it  nearly  reaches  the  strength  of  the  electro- 
lyte, when  it  is  added  to  the  tanks.  For  loss  of  solution  in- 
volved, see  page  39. 

Slime  washing. — The  slime,  as  removed  from  the  anodes, 
contains  a  large  amount  of  valuable  solution  which  is  stronger 
and  more  neutral  than  the  main  body  of  the  electrolyte.  Fil- 
tration and  washing  has  been  done  by  suction  filters,  filter 
presses  with  iron  plates,  and  decantation.  The  suction  fil- 
ter will  probably  not  come  into  use  any  more,  although  it 
is  successful.  The  slime  filters  very  well  in  a  press,  but  there 
are  difficulties  in  forcing  it  into  a  press,  on  account  of  lumps 
of  lead  that  stop  up  the  pipes.  Washing  by  decantation  is 
the  best  in  my  opinion.  To  secure  the  best  result,  the  wash- 
ing should  be  done  on  the  counter-current  principle.  One 
washing-tank  and  several  storage  tanks  for  various  strengths 
of  wash-water  comprise  the  necessary  apparatus,  with  a  steam- 
pipe  to  heat  the  slime  and  solution,  the  latter  making  it  break 
up  and  wash  better. 

Mr.  F.  C.  Ryan,  of  the  United  States  Metals  Refining  Co., 
made  an  experiment  as  follows,  which  shows  that  the  heating 
does  not  decompose  any  of  the  fluosilicic  acid. 

Equal  weights  of  raw  slime  were  stirred  with  equal  quan- 
tities of  hot  (180°  F.)  and  cold  water,  for  half  an  hour,  when 
the  wash- water  was  decanted  and  tested. 

As  will  be  seen  there  was  no  material  difference  in  the 
effectiveness  of  the  washing. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     247 

TABLE  90. 

Cold  Water  Hot  Water 

Sp.gr.  1.079  =  10. 5°  B  Sp.gr.  1. 083  =  11. 0°  B 

SiF6  =  2.95%  SiF8  =  3.0% 

Pb.  =   4.76%  Pb  =   4.94% 

Experiment  indicates  that  the  slime  is  readily  washed, 
and  no  absorption  or  retention  of  stronger  solution  takes  place 
when  the  slime  is  stirred  up  well  with  water  or  solution. 

I  have  worked  out  an  equation  from  which  may  be  closely 
calculated  the  effectiveness  of  washing  on  the  counter-current 
principle  with  four  washings. 

Let  a  =  percentage  of  acid  in  last  wash- water 
b  =         "          "     "    "  third 
c=         "          il     "     "  second     " 
d=         "          "     "    "  first 

x=         "          "     "    "  solution    to    be    washed    from 

slime. 

volume  wet  slime  after  settling 
Total  volume  after   adding  wash- water* 

The  equations  are: 


y 

b-a 
c= 

y 


a  —  c 

x"+c 


248  LEAD  REFINING  BY  ELECTROLYSIS. 

If  for  example  one  cubic  foot  of  slime  is  washed  with  1£ 
cubic  feet  of  water  2/=|.  The  acid  of  the  strong  solution 
is  about  20%,  so  I  have  taken  x=20.  In  this  case,  from  the 
above  equations: 

a  =  1.52% 
6  =  3.80% 
c  =  7.21% 
d=  12.33% 

This  shows  a  removal  of  all  but  7.5%  of  the  contained 
electrolyte,  or  say  1.3  Ibs.  SiF6  per  ton  of  lead.  The  amount 
of  wash-water  to  be  added  to  tanks,  above  the  volume  of  the 
slime  taken  out,  would  be  only  about  enough  to  make  up  the 
normal  evaporation  in  the  tanks,  taking  i/=f. 

If  y=$t  a=4.00%  =  3.2    Ibs.  SiF6  per  ton  lead 

y=j,  a=   .64%  =  0.5    Ibs.  SiF6    "     "     ll 

y  =  i}  a=   .17%=   .14  Ibs.  SiF6    "     "      " 

y=^}  a=   .06%=   .05  Ibs.  SiF6    "     "      " 

Plant  for  washing  is  shown  in  Fig.  55. 

A  single  plunger-pump  can  be  used  for  pumping  wash- 
water  from  the  storage  tanks  to  the  washing  tank.  The 
storage  tanks  are  at  a  lower  level,  so  the  clear  solution  may 
be  siphoned  off  directly.  The  storage  tanks  are  required  to 
hold  twice  as  much  as  the  washing  tank. 

Conductors. — Rolled  copper  conductors  are  used,  which 
may  be  either  nearly  square  in  cross-section  or  flat.  The  flat 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     249 

8 


Q)         Storage  for 
wash  water 


Siphon 
to  empty  washer 


FIG.  55. 


250  LEAD  REFINING  BY  ELECTROLYSIS. 

bars  cool  a  little  more  on  account  of  greater  surface,  increas- 
ing their  conductivity  slightly.  Conductors  are  either  placed 
on  top  of  the  tanks  or  at  the  side,  the  best  position  being  on 
top,  as  a  shorter  lug  may  be  used  on  the  electrodes.  A  bar 
1  or  1J  inches  thick  and  4  inches  wide  is  suitable.  Any  neces- 
sary bends  can  be  put  in  by  heating  the  bar  to  a  dull  red  at 
the  right  place,  when  the  bend  can  be  easily  put  in. 

Cranes. — The  three-motor  cranes,  though  more  expensive 
than  one-motor  cranes,  are  to  be  preferred.  Those  in  use 
have  about  a  50-foot  span  or  more  and  can  carry  ID  tons  nom- 
inally. Some  cranes  have  one  wire  hoisting-rope  and  one 
hoisting-drum,  and  others  have  a  rigid  construction  with 
heavy  guides  at  the  ends  of  the  electrode  racks  with  a  hoist 
at  each  end;  but  they  are  more  expensive,  although  working 
faster  than  the  single-rope  type.  The  cranes  carry  a  sepa- 
rate frame  with  hooks  for  lifting  electrodes,  the  point  of  en- 
gagement for  the  anodes  being  underneath  the  lug  just  in- 
side the  tank,  while  the  cathodes  may  be  lifted  at  various 
places  according  to  the  type  of  cathode. 

The  set  of  hooks  shown  in  Fig.  56  has  its  center  of  gravity 
too  near  the  hook  to  be  satisfactory,  but  it  was  made  this 
way  on  account  of  limited  head-room. 

The  tank-room  floor  has  a  fairly  large  space,  about  15  ft. 
or  more  in  width,  at  each  end  for  working  on  electrodes  and 
for  the  industrial  railway.  A  number  of  racks  for  holding 
fresh  anodes  properly  spaced  for  the  tanks  is  convenient. 
These  may  be  brought  from  the  melting-plant  best  by  a  crane 
which  commands  both  melting-  and  depositing-floors,  but  also 
on  the  industrial  railway.  A  form  of  rack  to  economize  space 
is  shown  in  Fig.  57.  Before  removing  the  lowest  set  of  anodes, 
the  I-beams  for  the  upper  set  are  lifted  out  of  the  way.  Three 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS      251 


252  LEAD  REFINING  BY  ELECTROLYSIS. 

sets  can  be  stacked  as  well  as  two.  The  cathodes  are  dumped 
on  flat  cars  to  be  taken  to  the  refinery  after  the  supporting 
bars  have  been  pulled  out. 

Floors. — The  floor  planking  is  not  nailed  down  at  places 
near  the  tanks,  to  facilitate  their  removal  when  cleaning  or 
when  repairs  are  necessary. 

Evaporators. — Wood  tanks  and  lead  pans,  with  a  steam- 
coil,  and  also  copper  pans,  have  been  used  for  evaporating. 
None  of  these  are  perfectly  satisfactory.  A  copper  pan  was 
used  at  Trail,  but  copper  was  dissolved  and  the  refined  lead 
contained  copper.  It  is  my  opinion,  though,  that  a  copper 
pan  can  be  used  successfully  by  properly  protecting  it  from 
dissolving.  This  can  be  done  by  having  metallic  lead  in  the 
solution  in  contact  with  the  pan.  Under  these  circumstances 
no  copper  could  dissolve  until  there  was  a  difference  of 
e.m.f.  between  the  lead  and  any  point  in  the  copper  pan  of 
about  .5  volt.  Another  method  would  be  to  hang  a  lead  pig 
in  the  evaporator,  connecting  the  pig  as  anode  and  the  pan 
as  cathode;  by  passing  a  small  current  the  pan  could  be  kept 
covered  wherever  wet  by  the  solution  with  a  little  lead,  and 
there  would  be  no  chance  for  copper  to  dissolve  on  account 
of  the  considerable  difference  of  dissolving  e.m.f.  between 
lead  and  copper. 

Of  course  the  acid  water  condensing  on  the  upper  part 
of  the  pan  could  dissolve  copper,  but  there  would  be  no 
trouble  in  curing  this  by  hanging  sheet  lead  around  the 
sides  of  the  pan. 

Wood  tanks  are  not  satisfactory  for  this  purpose,  while 
lead  pans  are,  though  they  do  not  last  long.  Their  life  can 
be  increased  by  hanging  sheet  lead  over  the  sides,  or  by  keep- 
ing a  small  current  passing  with  a  lead  pig  as  anode,  as  sug- 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     253 

gested  for  the  copper  pan,  so  that  the  tendency  is  to  thicken 
the  pan  instead  of  making  it  thinner. 

A  lead  steam-coil  is  satisfactory  as  a  means  of  heating  the 
solution.  The  lead  dissolves  from  the  coil  slowly,  but  this 
does  not  make  any  serious  difference.  At  Trail,  when  refin- 
ing 20  tons  per  day,  one  evaporator  20  inches  deep,  8  feet 
wide  and  10  feet  long,  was  sufficient  to  evaporate  the  wash- 
water  from  2  to  10°  B.  up  to  20°  B.  It  should  be  noted  that 
the  removal  of  the  slime  itself  reduces  the  volume  of  elec- 
trolyte in  the  refining  tanks,  and  as  this  slime  is  finally  re- 
moved wet  the  volume  of  the  contained  wash-water  should 
not  be  lost  sight  of  in  calculating  the  amount  of  evaporation 
necessary.  Some  evaporation  takes  place  from  the  lead  re- 
fining-tanks,  which  I  estimate  at  about  2.2  cu.  ft.  per  ton 
refined  per  day. 

The  stronger  wash-water,  if  possible,  should  be  added 
back  to  the  cells  without  being  heated,  and  only  the  weaker 
solutions  evaporated  to  save  losses  by  volatilization.  By  wash- 
ing the  slime  by  decantation,  and  a  carefully  arranged  method 
of  washing,  I  think  it  would  be  possible  to  get  along  with- 
out any  evaporation  at  all.  In  fact  this  was  done  at  Trail 
at  first  when  the  acid  loss  was  as  follows: 

Aug.      3d— Sept.  16th,  1903,  13.8  Ibs.  SiF6  per  ton  lead 
Sept.  16th— Oct.     6th,  1903,    7.7    "    SiF6   "     "     " 

Part  of  this  loss  was  due  to  absorption  and  leakage,  and 
no  adequate  means  for  collecting  leaks  was  provided. 

Regarding  the  amount  of  evaporation  from  the  deposit- 
ing tanks,  I  think  it  very  probable  that  with  a  well-syste- 
matized washing  plan,  the  evaporation  from  the  tanks  will 
take  care  of  all  or  almost  all  of  the  wash-water  it  is  necessary 


254  LEAD  REFINING  BY  ELECTROLYSIS. 

to  use.  Just  how  much  evaporation  takes  place  I  do  not  be- 
lieve has  been  determined,  because  of  the  difficulty  in  making 
such  a  determination  in  a  refinery.  We  have  certain  ways 
of  getting  at  this,  however.  The  voltage  between  electrodes 
in  the  solution  being  taken  at  .3,  this  is  a  measure  of  the  elec- 
tric energy  expended,  which  is  all  absorbed  in  heating  the 
solution,  and  this  serves  to  maintain  the  electrolyte  at  about 
30°  C.  while  the  temperature  of  the  room  is  probably  about 
17J0  C.  A  large  proportion  of  the  cooling  of  the  electrolyte 
is  undoubtedly  the  result  of  evaporation.  Taking  an  evapo- 
rative efficiency  of  only  50%,  the  volume  of  water  driven 
off  per  ton  lead  refined  per  day  would  be  about  2.2  cu.  ft.  On 
the  assumption  that  the  cooling  air  (that  is  the  tank-room  air 
in  this  case)  is  saturated  with  water,  and  that  it  escapes  from 
the  surface  of  the  liquid  three-quarters  saturated,  Hausbrand's 
tables*  give  for  air  temperature  15°,  and  water  temperature 
30°,  65%  of  the  heat  absorbed  by  evaporation,  and  35%  by 
heating,  and  for  20°  and  30°,  60%  by  evaporation  and  40% 
by  heating.  My  assumption  of  50%  still  allows  something 
for  heat  loss  through  the  sides  of  the  tanks,  especially  as  the 
tank-room  air  is  not  saturated  with  water  by  any  means, 
except  occasionally. 

This  will  easily  take  care  of  all  the  water  that  need  be 
used  in  washing  the  slime,  and  probably  of  all  the  wash- 
water  needed  altogether. 

One  cubic  foot  of  ordinary  bullion  gives  about  one  half 
cubic  foot  of  wet  slime  after  its  removal  from  the 
anode. 


*  Hausbrand,     "  Evaporating,    Condensing     and    Cooling     Apparatus," 
page  327. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     255 


TABLE  91. 


Plant. 

Present 
Capacity. 

Number 
of 
Tanks. 

Electrolyte 
Grams  per 
100  cc. 

Electrode 
Separation  . 

Current 
Density, 
Amperes 
perSq.Ft. 

1.  Consolidated  Mining 
and  Smelting  Com- 
pany of  Canada,  Trail, 
B.C. 

Approxi- 
mately 80 
tons  per  day 

240 

6-7  Pb 
12-13  SiFs 

4f  ins. 

16 

2.  United  States  Metals 
Refining  Company, 
Grasselli,  Indiana. 

Approxi- 
mately  85 
tons  per  day 

176 

7  Pb 
13  +  SiFe 

4f  ins. 

12-15  + 

3.  Newcastle  -  on  -  Tyne 
Plant.  Data  withheld 
at  request  of  owners. 

Plant. 

Anodes 
Active 
Surface. 

Average 
Volts 
per  Tank 

Percentage 
Anode 
Scrap. 

Cathodes. 

Anodes 
per 
Tank. 

Tank 
Arrange- 
ment. 

1.  Consolidated  Mining 
and  Smelting  Com- 
pany of  Canada,  Trail, 
B.C. 

26  X30£ 
ins. 
Weight 
350  Ibs. 

.30 

15  or  less. 

2  sets  for 
each  set 
anodes. 
Weight 
150  Ibs. 
each. 

20 

Cascade. 

2.  United  States  Metals 
Refining  Company, 
Grasselli,  Indiana. 

2X3  ft. 
Weight 
400  Ibs. 

.38 

25,  to  be 
reduced  to 

15%. 

2  sets. 
Weight 
150    to 
175  Ibs. 

28 

Walker 

System. 

Plant. 

Slime 

Treatment. 

Source 
of 
Power. 

Size  of  Tanks 
Inside. 

Genera- 
tors 

1.  Consolidated  Mining 
and  Smelting  Com- 
pany of  Canada.Trail, 
B.  C. 

Leaching  with  sodium 
sulphide   solution. 
Melting  residue  to  dore" 
after    oxidizing    sul- 
phides. 

Water. 

84^X30X44  ins. 

1-3500 
amperes, 
60-110 
volts. 

2.  United  States  Metals 
Refining  Company, 
Grasselli,  Indiana. 

Melting  to  slag,  matte 
and  dore". 

Steam. 

132X30X43  ins. 

1-4500 
amperes, 
60 
volts. 

Power  plant. — The  subject  of  power  plants  calls  for  no 
special  remarks  here,  as  more  accurate  information  on  that 
subject  that  I  could  give  can  be  got  elsewhere.  In  mak- 
ing estimates  of  refining  cost,  the  power  is  usually  consid- 
ered as  being  supplied  separately,  and  the  item  for  power 
includes  all  expenses,  interest,  and  depreciation  for  the  power 
plant. 


256 


LEAD  REFINING  BY  ELECTROLYSIS. 


Slime  plant. — All  the  apparatus  mentioned  is  not  appli- 
cable to  any  one  process. 

Drying  slime. — This  has  been  done  at  Trail  by  filling  into 
wheelbarrows  and  running  them  into  a  warm  brick  oven  and 
leaving  until  diy.  On  dumping  the  slime  into  a  brick  stall 
it  takes  fire  and  roasts  itself.  It  may  also  be  spread  on  an 
iron  floor,  or  even  in  a  lead  pan  gently  heated  from  under- 
neath. Apparatus,  as  shown  in  Fig.  58,  would  be  an  improve- 


FIG.  58. 

ment  on  the  above  methods.  The  heat  could  be  main- 
tained to  either  dry  the  slime  or  roast  it,  as  desired.  This 
apparatus  is  also  applicable  to  roasting  with  sulphuric 
acid. 

Melting  slime. — Magnesia-lined  reverbatory  furnaces  are 
most  used  for  high  temperature  work  in  melting  and  refining 
dore.  Most  varieties  of  crucibles,  including  graphite,  are 
rapidly  corroded  with  most  slime  mixtures.  Clay-lined  graphite 
.crucibles,  I  understand,  are  about  the  best  for  the  purpose. 
For  melting  slime  to  matte  and  slag,  or  metal,  matte  and 
slag,  iron  pots  are  quite  satisfactory,  though  there  is  some 
corrosion  of  the  pot  by  the  slag.  Pots  arranged  as  shown  in 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     257 

Fig.  59,  while  they  have  not  been  practically  tried,  could  not 
very  well  fail  to  work,  because  the  metal  and  matte  have  very 
little  or  no  action  on  iron  at  the  moderate  temperatures  used. 
For  melting  slime,  from  which  copper,  antimony,  and  ar- 
senic have  been  removed  by  wet  methods,  a  silicious  slag 


FIG.  59. 

should  be  produced  by  reacting  on  the  lead  sulphate  of  the 
slime  with  silica  which  is  added.  This  melting  can  be  easily 
done  in  crucibles,  as  no  furnace  refining  is  required. 

Leaching  slime. — The  treating  of  slime  with  ferric  sul- 
phate solution,  etc.,  can  be  done  in  lead-lined  stir-tanks. 
The  solution  can  be  afterward  removed  by  settling  and  siphon- 
ing off  the  clear  liquid.  Washing  can  be  done  by  decantation, 
or  a  lead-lined  montejus  may  be  used  to  force  the  solution 
into  a  filter-press.  At  this  period  of  operation,  filter-press- 
ing works  well. 

Leaching  with  hydrofluoric  acid  can  be  executed  in  the 
same  tank,  if  washing  by  decantation  has  been  resorted  to, 
or  in  a  smaller  tank  of  the  same  character  if  filter  cakes  are 
being  leached.  After  hydrofluoric  acid  has  been  applied  in 
excess,  the  insoluble  residue  becomes  flocculent  and  easily 
suspended,  so  that  agitation  by  air  would  be  successful  here. 
It  is  occasionally  necessary  to  add  metallic  antimony  to  pre- 
cipitate dissolved  silver,  which  happens  mainly  if  the  slime 


258  LEAD  REFINING  BY  ELECTROLYSIS. 

has  been  air-oxidized.  Placing  chunks  of  antimony  on  the 
bottom  of  the  tank  will  do,  but  suspending  them  with  copper 
wires  is  more  convenient. 

Filtration  of  the  antimony  fluoride  solution  is  quite  simple, 
but  the  solution  has  too  much  corrosive  action  on  metals,  ex- 
cept possibly  lead,  to  permit  the  use  of  anything  but  wood 
for  filters.  A  gravity  filter,  with  a  cloth  supported  on  per- 
forated lead  or  grooved  wood,  is  successful  though  slow. 

The  roasting  of  leady-copper  matte,  and  leaching  it  with 
iron  and  copper  sulphate  solution  containing  free  sulphuric 
acid,  is  directly  analogous  to  the  production  of  bluestone  from 
matte  and  sulphuric  acid.  The  most  successful  methods  and 
apparatus  appear  to  be  those  described  in  "The  Mineral 
Industry,"  Vol.  VIII,  page  189,  and  Vol.  X,  page  231,  by 
0.  Hofmann.  The  pulverizing  of  the  raw  matte  to  50  mesh 
is  done  by  a  Krupp  ball-mill,  the  roasting  in  a  two-story  Pearce 
furnace;  the  regrinding  is  an  easier  matter,  but  the  method 
is  not  described. 

The  dissolving  is  done  in  wood  stir-tanks  12  feet  in  diam- 
eter and  6  feet  deep,  with  a  12X1 2-inch  oak  paddle  for  stir- 
ring. A  truncated  cone  in  the  center  on  the  bottom  5  feet 
3  inches  diameter  across  the  top,  and  17  inches  high,  base 
7  feet  6  inches  diameter,  also  of  wood,  and  filled  with  sand, 
prevents  the  matte  from  piling  up  in  the  center  of  the  tank. 
After  reaction  is  complete,  the  mixture  runs  into  air-pressure 
tanks,  and  is  then  forced  into  wood  filter-presses,  though  hard- 
lead  pressures  ought  to  be  much  better. 

The  slightly  acid  solution  is  neutralized  with  a  little  more 
matte  in  a  deep  tank  with  air-blast  for  agitation,  to  remove 
iron,  arsenic,  antimony,  etc.  In  the  present  case,  however, 
the  ferrous  sulphate  present  is  desired,  so  sufficient  neu- 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     259 

tralization  to  remove  arsenic,  antimony,  bismuth,  and  silica 
without  oxidation,  is  only  needed,  with  no  oxidation. 

Electrolytic  antimony  depositing  tanks.  —  Lead-lined 
wooden  tanks  well  painted  are  in  use  and  answer  well,  though 
a  sulphur-treated  concrete  tank  is  probably  better.  The 
solution  should  be  cooled  with  a  coil  of  lead  pipe,  through 
which  water  is  circulated,  connection  being  made  thereto 
through  a  long  hose  to  prevent  grounding  the  circuit. 

The  anodes  for  depositing  antimony  consist  of  soft  lead 
rods  about  three-eighths  inch  in  diameter,  wrapped  in  two  or 
three  thicknesses  of  muslin.  They  are  merely  suspended  from 
copper  cross-bars  at  a  distance  of  three  inches  apart.  These 
cross-bars  can  be  covered  with  lead  or  rubber.  In  the  latter 
case  the  rubber  is  cut  away  at  the  places  where  the  lead 
rod  comes  in  contact  with  the  cross-bar. 

The  cathodes  consist  of  sheet  copper,  which  have  been 
slightly  greased  to  facilitate  the  removal  of  the  deposited  an- 
timony. The  cathodes  have  a  certain  small  disadvantage, 
for  if  they  are  sufficiently  greased  to  permit  the  easy  removal 
of  the  antimony,  the  antimony  is  likely  to  drop  off  to  some 
extent  in  the  tanks,  as  it  curls  away  from  the  cathodes,  and 
if  they  are  not  greased  enough  the  cathodes  have  to  be  bent 
and  wrinkled  to  get  all  the  antimony  off.  It  is,  however,  not 
necessary  to  get  all  the  antimony  off  each  time,  and  if  pieces 
fall  in  the  tanks  they  can  be  readily  collected.  A  current 
density  of  15  amperes  per  square  foot,  volts  about  2.9  to  3.0, 
and  a  distance  from  center  to  center  of  cathodes  of  about  4 
inches  may  be  recommended,  though  this  can  perhaps  be  im- 
proved upon. 

Wrapping  the  anodes  should  be  done  with  muslin  strips 
put  on  diagonally,  with  a  string  or  elastic  band  around  each 


260 


LEAD  REFINING  BY  ELECTROLYSIS. 


end  to  hold  it.  The  anodes  should  not  be  allowed  to  dry  with 
acid  on,  as  this  rots  the  cloth;  nor  should  the  solutions  be  too 
strong  or  contain  too  much  sulphuric  acid,  for  the  same  rea- 
son. The  best  way  to  do  is  to  keep  the  anodes  in  use  as  con- 
tinuously as  possible,  and  if  the  tank  has  to  be  shut  down,  fill 
it  with  water.  The  anode  scrap  can  be  thrown  into  the  lead- 
furnace  of  course,  cloth  and  all.  The  production  of  antimony 
is  small,  so  that  individual  handling  of  electrodes  with  a 
block  attached  to  an  overhead  trolley  parallel  to  the  long 
side  of  the  tanks  is  all  that  is  necessary.  The  form  of  tank 
is  shown  in  Fig.  60. 


=3 

| 

z-rr^ 

- 

"I 

.      __^         1 

X^. 

^—  —  =3         1 

_— 

.'          •  ,           -—  ^ 

•<•  •  ^'"  j;  jj 

j  . 

Z21 

IG, 

60. 

Electrolytic  ferric  sulphate  tanks. — The  chemical  and 
electrochemical  side  of  ferric-sulphate  production  has  been 
treated  elsewhere.  In  constructing  the  electrolytic  tanks,  the 
following  diaphragms  are  available  and  practical:  Perfor- 
ated lead  sheets  in  pairs  with  asbestos  paper  or  asbestos  board 
between;  perforated  wooden  boards  with  the  holes  closed 
with  asbestos,  and  hardened  asbestos  mill-board.  All  may 
be  used  interchangeably  as  diaphragm  plates.  From  the 
electrical  standpoint,  the  lead  diaphragm  is  the  best,  on  ac- 
count of  the  low  resistance  of  these  diaphragms  consequent 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     261 

on  the  large  relative  area  of  the  holes,  while  the  hardened 
asbestos  board  has  the  greatest  resistance.  The  resistances 
have  not  been  accurately  measured,  but  Table  92  (page  262), 
from  tanks  of  various  sizes  in  operation,  is  of  interest. 

Of  the  above  tanks  all  but  No.  2  gave  high  current  effi- 
ciency; No.  2  had  internal  leaks  and  gave  a  low  efficiency. 

Fig.  61  illustrates  a  tank  for  3500  amperes.  The  cathode 
bus  bar  runs  lengthwise  in  the  center  of  the  tank,  and  a  cath- 


FIG.  61. 

ode  is  placed  on  each  side  in  each  compartment.  The  anodes 
are  of  Acheson  graphite  one  inch  in  diameter,  spaced  1J  inches 
centers.  The  anodes  are  inserted  in  the  channel  irons,  and 
cast  in  lead,  which  makes  a  good  contact.  The  sheet-copper 
cathodes,  cross  bars,  and  lead  lining  of  the  tank  call  for  no 
special  remark.  The  circulation  of  the  anolyte,  which  is  quite 


262 


LEAD  REEINING  BY  ELECTYOLYSIS. 
TABLE  92. 


Diaphragm. 

Date. 

Separation                       Diaphragm. 

Holes. 

Holes 
Center  to 
Center. 

1.  Wood     and 
Asbestos. 

Sept. 
1903 

3"  centers.             f"    wood,    bored,    and    holes 
filled  with  asbestos. 

4" 

2.  Wood     and 
Asbestos. 

1905- 
1906 

3£"  centers.           f"    wood,    bored,    and    holes 
filled  with  asbestos. 

i" 

14" 

3.  Lead       and 
Asbestos. 

June, 
1906 

4^                             2i   Ib.   lead    sheets,    asbestos 
paper  between. 

1" 

1" 

average. 

4.  Sulphurized 
Asbestos. 

1906 

3f                             J"    asbestos,    with    absorbed 
sulphur. 

5.  Sulphurized 
Asbestos  . 

1906 

3J                             i"    asbestos,    with    absorbed 
sulphur. 

Diaphragm. 

Date. 

Compartments. 

No 
Com- 
part- 
ment. 

Active 
Cathode 
Area. 

Solution. 

Temper- 
ature. 

1.  Wood     and 
Asbestos. 

Sept. 
1903. 

18"X13"X3" 

11 

13.8  sq.ft. 

3%  H2S04 
4%  Fe'^  +  Fe" 

28°  C. 

40°  C. 
41°  C. 

Wood     and 
Asbestos. 

1905- 
1906. 

33"  X5  ft. 

23 

260  sq.  ft. 

3.4%  H2SO4 
4    %  Fe" 
3    %  Cu 

40°  C. 
50°  C. 

3.  Lead       and 
Asbestos. 

June, 
1906. 

3TX2WXW 

3 

3.  33  sq.ft. 

3^5  %  Fe 
3.75%  Cu 

62°  C. 

4.  Sulphurized 
Asbestos. 

1906. 

33"  X23" 

7 

24  sq.  ft. 

4-5%  H2SC-4 
4%  Fe 
3%  Cu 

40-50°  C. 

5,   Sulphurized 
Asbestos. 

1906. 

33"  X23" 

7 

24  sq.  ft. 

4-5%  Fe" 

44°  C. 

Diaphragm  . 

Date. 

Am- 
peres. 

v*.  «• 

s&s: 

1.    Wood    and 
Asbestos. 

Sept. 
1903. 

115 

100 
90 

2.25        8  3 

1.60        7.25 
1  .  50        6.5 

Amor-            Polarized  stationary  anodes, 
phous. 
Carbon.         Clean    anodes,    moving,    no 
polarization. 

2.  Wood     and 
Asbestos. 

1905- 
1906 

2000 

2.0        7.7 

Graphite.      No    polarization.       Internal 
leaks.     Poor  efficiency. 

3.  Lead       and 
Asbestos. 

June, 
1906. 

8. 
33. 

200- 
240 

1.             10.0 
1.7 

Graphite.      Normal    conditions    of    cur- 
rent and  voltage. 

4.  Sulphurized 
Asbestos. 

1906. 

2.4?      8.3-10 

Graphite.      Copper-slime  treatment. 

5.  Sulphurized 
Asbestos  . 

1906. 

140 

1.6        5-8 

Graphite.      Lead-slime    treatment.     Sil- 
ica in  solution  and  anodes 
afterward  polarized. 

REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     263 


vigorous  between  the  various  anode  compartments,  and  of 
the  catholyte  which  circulates  freely  around  all  cathodes, 
is  maintained  by  two  separate  air-lifts,  one  for  catholyte 
and  one  for  anolyte.  The  diagrams,  Fig.  62,  will  explain  the 
circulation. 

The  tank  is  operated  continuously,  and  the  anolyte  and 
catholyte  do  not  change  in  composition,  the  maintenance 
at  a  practically  constant  composition  being  assured  by  the 
continual  inflow  of  fresh  solution. 

The  inflowing  solution  contains  about  3%  of  copper  and 
5%  of  ferrous  iron,  beside  2  to  5%  of  sulphuric  acid.  The 


Air  Lift 


4-C — = 


M 


H-€ 


•-€ 


Cat  Holy  to 



1 

Anolyte 

— 

- 

s 

Anolyte 

1 

s 

Anolyte 

(^  — 
Catholyte               V 

=£ 

* 

ANOLYTE  CIRCULATION  CATHOLYTE  CIRCULATION 

FIG.  62. 

catholyte  contains  about  f  %  of  copper  and  the  same  amount 
of  ferrous  iron  and  acid. 

The  level  of  the  catholyte  is  higher  than  the  anolyte  by  a 
half  inch  or  so,  depending  on  the  diaphragm,  and  the  result  of 
constant  feed  of  fresh  solution  is  that  catholyte  continuously 
flows  in  a  small  stream  or  percolates  to  the  anolyte,  which 
assays  about  the  same  in  free  acid  and  copper  as  the  catho- 
lyte, but  contains  only  0.8-1.0%  of  ferrous  iron,  the  rest  being 
ferric  iron.  The  result  of  continuous  feed  is  of  course  con- 
tinuous overflow  of  finished  ferric  sulphate  solution,  through 
a  run-off  pipe  provided  therefor. 


264 


LEAD  REFINING   BY  ELECTROLYSIS. 


FIG.  63. 


In  putting  the  tank  together,  the  main  point  is  not  to  have 
any  internal  leaks  from  catholyte  to  anolyte  and  vice  versa. 
There    is   no  difficulty    about    this    if   the    following   method 
is  adopted.     In   the   first   place   the  dia- 
phragms,   if    of    wood,    are    of    separate 
boards,    which    should    be    tongued    and 
grooved.     These  boards  fit  between  two 
frames,  one  on  each  side.     A  small  piece 
of    round    asbestos    packing    should    be 
tacked  on  the  distance  frames,  with  small 
brads,    before    placing    the    diaphragms. 
When    the   whole   is  driven   together  by 
the    end    wedges,    this    makes    a    good 
joint.      See    Fig.    63. 

The  lift  required  to  circulate  the  solution 
is  only  about  3  inches  at  most,  and  the 
height  can  be  easily  got  with  a  3- foot  depth 
of  solution  in  the  air  and  solution  pipe. 

The  siphons  for  feeding  anolyte  to  and 
from  the  various  compartments  are  rather 
hard  to  manage  and  keep  working  unless 
provided  with  a  small  pipes  at  the  top  for 
drawing  air  out,  as  in  Fig.  64.  The  anode 
connection  may  be  made  by  a  copper  bar 
lying  on  the  center  of  the  anode  frame,  di- 
rectly over  the  cathode  bus  bar,  with  large 
wires  attached  over  each  channel-iron  and 
with  the  other  end  buried  in  the  lead- 
A  flexible  connection  is  required  of  course 
from  the  anode  bus  bar  to  the  outside  source  of  current. 
The  anolyte  is  a  little  heavier  than  the  catholyte,  and  by 


FIG.  64. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     265 

supplying  the  necessary  heat  to  the  anolyte,  this  may  be  cor- 
rected a  little  by  its  greater  heat  expansion,  thus,  diminish- 
ing the  tendency  for  mixing,  existing  especially  in  deep  tanks. 

A  lead  pipe,  heated  by  steam,  lying  in  one  of  the  anolyte 
troughs  at  the  side  of  the  tank  does  the  heating  well.  A  piece 
of  1J  pipe,  6  ft.  long,  is  enough  for  a  large  tank. 

Fig.  65  shows  a  smaller  tank  for  250  amperes.  The 
hardened  asbestos  diaphragms  are  38  by  25  inches.  By 
increasing  these  to  40  by  40  inches,  and  putting  more  com- 
partments into  the  tank,  it  could  be  easily  extended  to  take 
2000  or  3000  -  amperes.  The  diaphragms  are  made  as  follows: 
Powdered  sulphur  is  sifted  evenly  over  the  surface  of  }-inch 
asbestos  mill-board  in  the  amount  -required,  namely,  about 
I  Ib.  of  sulphur  per  square  foot  for  a  sheet  of  this  thickness. 
The  sheet  is  then  slid  into  an  oven  heated  by  an  oil  bath  to  a 
temperature  of  120-140°  C.  for  one  or  two  hours,  or  until  all  the 
sulphur  has  melted  and  soaked  in.  The  sheet  is  taken  out, 
cooled,  and  an  equal  amount  of  sulphur  put  on  the  other  side 
and  heated  again.  The  board  is  cooled  on  a  perfectly  flat 
floor,  and  makes  a  hard,  slightly  elastic  and  waterproof 
product. 

Before  putting  the  diaphragms  into  the  electrolytic  tanks, 
they  ought  to  be  soaked  about  two  weeks  in  very  dilute  sul- 
phuric acid,  as  some  expansion  takes  place  at  first.  Other- 
wise the  sheet  will  warp  in  the  tank.  The  method  of  assem- 
bling and  packing  the  joints  is  the  same  as  for  the  tank  just 
described.  This  construction  and  diaphragm  gives  a  tank 
which  is  so  tight  internally  that  it  allows  no  mixing  of  anolyte 
and  catholyte,  even  if  there  is  a  considerable  difference  in 
level  between  the  two,  and  it  is  necessary  to  use  a  small  siphon 
to  keep  catholyte  always  flowing  to  the  anolyte. 


266 


LEAD  REFINING  BY  ELECTROLYSIS. 


CQ 


Storage  capacity  should  be  provided  at  a  higher  level  to 
hold  sufficient  solution  to  feed  the  tanks  for  36  to  48  hours. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     267 

and  at  a  lower  level  to  receive  the  overflow  for  the  same  time. 
The  iron  in  the  solution  should  not  be  less  than  5%  and  could 
very  likely  be  6  or  7%,  though  this  has  not  been  attempted 
yet.  The  ferrous  iron  in  the  overflow  should  be  0.8  to  1.0%, 
the  remainder  being  ferric  iron.  With  50  gr.  total  iron  per 
litre  1000  amperes  produces  about  45  cubic  feet  per  day  per 
tank  containing  10  gr.  ferrous  iron  per  1000  cc. 

Electrolytic  tanks,  depositing  copper  from  sulphate  solu- 
tion with  insoluble  lead  anodes  and  no  diaphragm,  are  too 
simple  to  call  for  much  remark.  In  the  execution  of  the  fer- 
ric sulphate  process,  after  neutralizing  with  matte,  electro- 
lysis of  the  solution  with  a  lead  anode,  until  a  few  per  cent 
of  free  sulphuric  acid  is  present,  could  be  practiced,  and 
would  be  more  economical  unless  sulphuric  acid  was  very 
cheap. 

Refinery  operation  and  costs. — The  tank-room  opera- 
tions can  be  arranged  so  that  little  labor  is  required  on  Sun- 
day or  at  night.  The  daily  operation  includes  charging  and 
emptying  a  certain  number  of  tanks  and  drawing  cathodes 
and  replacing  them  in  an  equal  number  of  other  tanks,  the 
practice  being  to  make  two  sets  of  cathodes  from  each  set 
of  anodes.  The  operation  of  changing  cathodes  is  simple, 
but  requires  care  to  keep  the  old  cathodes  from  wiping  slime 
from  the  anodes  as  they  are  pulled  out,  and  the  new  cathodes 
on  account  of  their  usual  flimsy  character  have  to  be  handled 
delicately.  In  view  of  the  greater  ease  of  handling  and  supe- 
rior electrical  and  chemical  results,  I  believe  a  steel  cathode, 
as  described  on  page  228,  with  wooden  strips  1  inch  square 
having  a  groove  on  one  side,  slipped  over  the  edges,  ought 
to  be  used,  though  they  are  not  now.  These  strips  may  be  seen 
in  the  photograph,  Plate  7. 


268  LEAD  REFINING  BY  ELECTROLYSIS. 

Grooves  around  the  plates  will  take  the  place  of  wood 
strips.* 

It  is  necessary  to  inspect  the  tanks  with  a  voltmeter  to 
detect  short  circuits,  and  any  short-circuited  plates  are  taken 
out  and  straightened. 

At  Trail,  B.  C.,  after  removing  the  cathodes,  the  anodes 
are  taken  out,  a  tank-load  at  a  time,  and  the  anode  slime  is 
removed  in  separate  tanks,  by  wiping  the  scrap  with  rubbers 
and  pouring  water  on  afterward  to  clean  off  the  muddy  solu- 
tion. Another  way  is  to  hang  the  whole  tank-load  in  a  special 
tank  to  receive  the  slime,  and  reach  down  between  the  plates 
with  wipers  to  loosen  the  slime,  after  which  a  spray  is  turned 
on  the  plates.  This  is  quite  readily  done,  but  apparatus  shown 
in  Fig.  54,  is  believed  to  be  better  yet,  although  not  yet  in 
use.  This  apparatus  will  clean  a  whole  tank-load  at  once,  after 
which  they  may  be  sprayed  with  a  set  of  spray-pipes. 

After  the  anodes  have  been  taken  from  the  tank,  the  cir- 
culation of  electrolyte  is  shut  off,  by  connecting  the  overflow  of 
the  tank  next  above  and  the  feed  of  the  one  next  below  with 
a  hose.  The  clean  solution  is  then  siphoned  from  the  tank  into 
a  launder  beneath  the  tanks  which  carries  the  solution  to  the 
storage  tank.  The  workman,  with  rubber  boots  on,  next  gets 
into  the  tank  and  shovels  the  slime  into  a  barrel.  This  is 
more  troublesome  and  less  satisfactory  than  sluicing  the  slime 
into  a  car  beneath  the  tank,  because  the  tank  should  be  abso- 
lutely clean  when  solution  is  next  admitted.  Otherwise  the 
remaining  slime  is  stirred  up,  which  is  a  bad  thing  for  the 
cathodes.  It  should  be  remarked,  however,  that  it  is  not 
necessary  to  clean  out  a  tank  at  the  end  of  each  run  as  a  gen- 

*U.  S.  Patent,  Elliott  and  Kishner,  683283.     October  12,  1901. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.    269 

eral  thing,  for  most  or  all  the  slime  comes  out  on  the  anode 
scrap,  unless  the  anode  bullion  is  unusually  pure.  Usually 
the  anode  hardly  changes  its  appearance  during  the  whole 
depositing  operation.  To  fill  the  cleaned  tank,  it  is  only  neces- 
ary  to  run  a  hose  to  it  from  the  high-level  storage  tank  and 
start  the  solution  by  opening  a  valve  or  by  siphoning.  The 
temporary  hose  to  carry  the  circulating  solution  around  that 
tank  is  then  disconnected  and  taken  away. 

The  cathodes  are  best  washed  by  spraying  with  warm  or 
hot  water,  though  they  have  also  been  washed  by  dipping 
into  a  tank  containing  wash- water.  If  the  wash- water  is 
used  over  and  over,  until  it  reaches  the  strength  of  the  tank 
solution,  there  is  a  loss  of  solution  of  course,  as  it  will  not 
all  drain  off.  The  amount  of  solution  that  it  takes  to  wet 
the  cathodes  varies  of  course  with  the  cathode  thickness  and 
roughness.  With  the  samples  shown  in  Plates  2  and  3,  pages 
38  and  39,  the  amount  required  to  wet  them,  and  corre- 
sponding acid  loss,  with  the  weight  of  cathodes  per  square 
foot,  is  given  in  Table  93. 

TABLE  93. 


No.  in 
Photo- 
graph. 

Weight  per 
Square  Foot. 

Solution 
on 
Cathode. 

Acid  Loss 
per  Ton  Lead. 

Actual  Loss. 

Remark. 

2 

28.8  Ibs. 

•5  % 

1.661bs.  SiF6 

.83  Ibs.  SiF6 

Average  cathode. 

4 

22        " 

.39% 

1.33   "    SiF6 

.67    "    SiF6 

Average  cathode. 

5 

16        " 

.36% 

1.2     "    SiF6 

.60   "    SiF6 

Unusual  cathode. 

6 

1.1     " 

.22% 

.76   "    SiF6 

.38    "    SiF6 

Unusual  cathode. 

Not  well  wetted. 

The  actual  loss,  if  the  cathodes  are  first  washed  with  wash- 
water,  and  this  is  used  over  and  over  until  the  same  strength 
as  electrolyte,  would  be  one-half  the  loss  if  the  cathodes  are 


270  LEAD  REFINING  BY  ELECTROLYSIS. 

merely  drained.  At  7J  cents  per  pound  of  SiF6  the  maximum 
saving  is  so  small,  that  a  more  systematic  method  of  washing 
would  not  be  apt  to  pay.  The  amount  of  wash-water  to  be 
returned  to  the  tank  by  this  method  equals  the  amount  taken 
out  on  the  cathodes,  so  no  evaporation  is  required. 

The  surface  of  the  anode  scrap  is  only  from  one-third  to 
one-half  that  of  the  two  crops  of  cathodes  for  each  anode, 
and  the  anode  scrap  is  smoother  too,  so  that  the  acid  loss  from 
solution  and  wash-water  required  to  wet  anode  scrap,  is  about 
30  to  40%  of  that  on  the  cathodes. 

The  acid  loss  in  fairly  well-washed  slime  depends  some- 
what on  the  amount  of  slime  For  an  average  grade  of  bul- 
lion containing  96-97%  of  impurity,  the  loss  in  fairly  washed 
slime  will  not  exceed  2  Ibs.  SiF6  per  ton  of  lead,  so  that  the 
total  losses  on  and  in  material  removed  will  not  exceed  about 
3.1  Ibs.,  if  it  is  that  high.  When  it  comes  to  evaporation,  which 
is,  however,  not  absolutely  necessary,  there  is  a  chance  of  boil- 
ing off  acid. 

The  anode  scrap  and  cathodes  are  usually  carried  by  the 
crane  directly  to  the  melting-pots  and  dumped  in,  the 
cathode  cross-bars  of  course  being  first  pulled  out. 

For  disconnecting  tanks  from  the  electric  circuit  while 
cleaning  them,  a  small  copper  block  and  a  clamp  is  all  that 
is  necessary.  For  disconnecting  one  tank  it  is  usual  to  place 
copper  rods  across  from  side  to  side,  resting  on  the  conductors 
on  each  side  of  the  tank.  Sometimes  the  cathode  supporting- 
bars  can  be  used,  but  usually  they  are  too  short  to  reach,  and 
a  few  bars  of  special  length  are  necessary. 

The  tank  inspector  has  a  voltmeter  supported  by  straps 
around  the  neck  and  shoulders  so  that  it  lies  open  in  front 
of  him.  The  leads  are  connected  to  a  pair  of  small  ice-picks. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.    271 

With  one  in  each  hand,  the  voltage  of  all  the  cathodes  in  a 
tank  can  be  quickly  read.  Any  short  circuits  may  be  indicated 
by  chalk  marks,  to  be  fixed  by  moving  the  electrodes  slightly, 
or  if  necessary,  by  taking  the  cathodes  out  and  straightening 
them. 

Slime  is  variously  washed  by  decantation,  and  by  filter- 
pressing.  The  results  obtained  by  washing  by  decantation, 
are  mentioned  on  page  247.  In  washing  anode  slime  by  decan- 
tation, if  hot  wash- water  is  used,  the  slime  breaks  up  better 
and  is  more  rapidly  mixed  with  the  wash-water. 

Elevating  slime  either  to  washing-tanks,  or  to  a  filter-press, 
should  not  be  attempted  by  a  montejus,  this  having  been  a 
partial  failure  several  times.  It  ought  to  be  mechanically  ele- 
vated in  tanks,  or  driven  through  a  good-sized  iron  pipe  with 
a  pump.  The  former  of  these  two  methods  was  in  use  at  Trail 
at  first,  and  is  sure,  though  clumsy. 

The  various  wash-waters  from  cathodes  and  anode  scrap 
should  be  filtered  and  run  to  a  storage  tank,  and  then  evaporated 
if  necessary.  The  strong  wash-water  from  the  slime  can  go 
directly  to  the  electrolyte  storage  tanks. 

Making  cathodes,  as  invented  by  Dr  Wm.  Valentine  (see 
page  231),  requires  one  man,  who  makes  and  hangs  at  least 
10  sheets  an  hour.  One  man  can  make  400  sheets  of  the 
kind  used  at  Trail,  or  enough  for  30  tons  of  lead,  in  a  day,  and 
in  eight  hours  two  men  can  hang  and  straighten  the  same 
number  of  sheets,  so  that  the  cost  for  sheets,  with  labor  at 
$2.00,  is  about  20  cents  per  ton.  The  cost  for  Valentine 
cathodes  is  then  a  little  higher,  but  they  have  certain  advan- 
tages over  the  old  style,  in  giving  better  and  more  uniform 
contacts,  and  the  lugs  being  made  thicker  than  the  plate  itself, 
reduces  very  much  the  liability  of  the  cathodes  being  cut 


272 


LEAD  REFINING  BY  ELECTROLYSIS. 


through  by  the  electrolyte  at  the  surface,  and  dropping  in 
the  tanks.  To  prevent  this  with  the  old  style  of  cathodes,  a 
streak  of  asphaltum  paint  was  put  on  where  the  surface  of 
the  solution  comes.  There  is  no  doubt  but  what  the  molds 
for  making  Valentine  cathodes  can  be  improved  so  as  to  save 
considerable  labor. 

The  labor  cost  for  operating  tanks,  that  is,  charging  and 
drawing  and  washing  and  cleaning  electrodes,  cleaning  tanks 
(on  the  supposition  that  the  slime  is  sluiced  out  into  a  car 
underneath),  inspecting  tanks  and  fixing  short  circuits,  hand- 
ling anode  scrap  and  weighing,  may  be  taken  in  detail  as  fol- 
lows, for  a  production  of  100  tons  lead  per  day: 


TABLE  94. 

Charging  tanks 4  men  8  cents  per  ton. 

Emptying  tanks 4  8 

Cleaning  tanks 4  8 

Inspecting  tanks 9  ,3  shifts,  18 

Weighing  and  tramming 3  6 

Cleaning  and  handling  scrap 4  8 

Repairs 2  6 

Making  and  straightening  sheets 10  20 

Other  operations 2  4 


Total  tank-room  labor. . .  .42  men 


86  cents  per  ton. 


By  the  use  of  steel  cathodes  I  believe  this  cost  can  be 
reduced  to  about  60  cents  per  ton,  by  removing  the  necessity 
of  making  starting  sheets  and  of  much  inspecting,  beside  im- 
proving results. 

The  labor  cost  of  loading  pig  lead  and  unloading  bullion, 
sampling,  weighing  and  tramming  to  and  from  melting  plant, 
would  be  about  19  cents  per  ton  refined. 

In  the  melting  plant,  about  100  Ibs.  of  coal  or  less  is  used 
per  ton  of  lead  refined.  The  labor  cost  charging  the  kettles 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     273 

and  molding  anodes  and  lead  and  stacking  the  anodes,  is  about 
as  follows: 

TABLE  95. 

Charging  furnaces  with  lead,  and  skimming 10  cents  per  ton  refined. 

Molding  lead,  including  firing 9      "       "      " 

Molding  anodes  and  stacking,  including  firing 13      "       "      "         " 

Repairs,  including  new  pots 6     ' '       "      "         " 

Coal.  .  .   10     "       "      " 


48  cents  per  ton  refined. 

It  might  be  of  interest  to  state  the  approximate  labor  cost 
when  handling  electrodes  singly  with  an  overhead  trolley, 
hoisting  being  done  by  a  chain  block,  on  a  scale  of  10  tons 
per  day. 


TABLE  96. 


Unloading  anodes  from  cars 

Tramming  to  tank-room 

Straightening  and  charging  anodes. 

Making  starting  sheets 

Inspecting  and  night  man 

Charging  cathodes 

Drawing  and  washing  cathodes.  . . . 
Drawing  and  cleaning  anode  scrap. 

Molding 

Loading  on  cars 

Unclassified. . 


6  cents  per  ton  refined. 


4 

a      t 

t         " 

30 

tt 

1  1 

25 

1  1 

it 

45 

tt 

tt 

8 

(t 

ti 

12 

1  1 

1  1 

40 

(i 

tt 

25 

(i 

tt 

10 

1  1 

1  1 

40 

t  ( 

t  ( 

Total  tank-room  labor  cost $2 . 45  cents  per  ton  refined. 


The  anodes  are  supposed  to  come  to  the  refinery  already 
cast,  and  merely  need  straightening.  The  figures  are  per  ton 
refined  lead  produced,  assuming  a  wage  of  20  cents  an  hour. 
The  labor  could  be  reduced  considerably. 


274  LEAD  REFINING  BY  ELECTROLYSIS. 

Comparative     Costs    of     Refining    by    the    Parkes    and    Betts 

Processes. 

Parkes  Process. — Assuming  that  all  approved  labor-saving 
machinery  is  used,  that  the  bullion  contains  .7%  Sb,  .8%  Cu, 
and  75  ozs.  silver  with  a  little  gold,  coal  at  $2.50  and  coke  at 
$5.00,  zinc  at  6  cents,  and  a  production  of  100  tons  per  day 
average  wages  $2.00  per  day: 

TABLE  97. 

400  Ibs.  coal  per  ton  bullion  received  at  works $0 . 50 

65  Ibs.  coke  for  reducing  hard  lead,  retorting,  etc 0. 16 

Zino,  16  Ibs 0 . 96 

Repairs  and  supplies 0.25 

Parting  and  refining  silver  and  gold 0.19 

Fluxes 0. 11 

Labor,  softening  and  desilverizing 0 . 23 

Labor,  retorting 0 . 07 

Labor,  cupelling 0 . 05 

Labor,  power  plant 0.14 

Labor,  working  by-products 0 . 34 

Foremen  and  general  labor 0 . 40 

Mechanics  and  helpers 0. 18 

$1.41 

Labor,  except  parting  plant $1 . 41 

Refining  charge  on  12  Ibs.  copper 0 . 09 

$3.67 

No  published  detailed  costs  of  refining  as  it  is  done  at 
present,  exist  as  far  as  I  know.  The  above  are  compiled  from 
various  sources  of  published  and  private  information.* 

The  above  assumptions  may  be  criticised  on  the  ground  of 
too  high  a  percentage  of  copper  in  the  bullion.  With  .2-. 3% 
of  copper,  the  costs  would  be  about  15  cents  less. 


*  I  am  much  indebted  to  Mr.  Ernst  F.  Eurich  for  figures  which  have 
been  largely  used  in  compiling  the  above  statement. 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     275 

Betts  Process  costs  on  same  bullion,  with  the  same  assumed 
cost  of  coal  and  labor: 

TABLE  98. 

Power  7-6  H.P.  days  total  at  $50  per  E.H.P.  year $1 . 06 

Tank-room,  platform,  and  repair  labor 0 . 86 

Melting  lead,  labor,  supplies,  repairs 0 . 38 

Coal  for  melting  lead 0.13 

Chemicals,  6  Ibs.  SiF6,  at  6  cents $0.36 

I    "    glue 07  0.43 

Slime  treatment,  except  power  and  assaying,  including  parting....  0.96 

$3.82 
Credit  about  20  Ibs.  electrolytic  copper  recovered  from  matte  at  3  cents      .  60 


Net  cost $3 .22 

For  a  complete  comparison  of  the  two  processes  it  is  neces- 
sary to  take  into  account  the  metal  losses,  interest  on  plant, 
and  general  expenses.  The  lead  loss  in  the  electrolytic  process 
is  practically  none,  as  even  the  lead  in  the  slime  is  returned 
to  the  lead  blast-furnace.  Five  pounds  lead  per  ton  is  an 
outside  estimate  of  loss.  The  zinc  process  will  lose  about  1% 
of  the  actual  lead  present.  The  antimony  loss  is  respectively 
10%  or  less  and  40%,  while  the  electrolytic  antimony  from 
the  electrolytic  process  is  also  usually  more  valuable  than 
antimony  in  hard  lead.  The  silver  loss  should  be  calculated 
on  actual  contents,  which  is  1|%  greater  (about)  than  that 
shown  by  commercial  fire-assay.  There  is  no  opportunity  for 
appreciable  silver  loss  in  the  electrolytic  process,  while  with  the 
zinc  process  the  loss  ascertained  from  various  sources  of  infor- 
mation may  be  taken  at  1%  as  an  average  for  good  work.  The 
same  figure  can  be  certainly  surpassed  by  the  electrolytic 
process,  but  lacking  clean-up  figures  from  lead  refineries,  I 
assume  the  same  figure  for  silver  loss  for  the  electrolytic  process 
as  for  the  zinc  process. 


276 


LEAD  REFINING  BY  ELECTROLYSIS. 


TABLE  99. 


Parkes  Process. 

Betts  Process. 

Net  working  cost.  . 

$3   67 

$3  29 

Interest  on  plant  at  10%*  

55 

55 

Lead  loss,  at  5  cents  per  Ib.  .  . 

1  00 

25 

Antimony  loss,  at  15  cents  per  Ib.  ..  . 

84 

21 

Interest  on  metal  in  process,  at  $150  per  ton, 
at  6%.                    

10 

24 

Interest  on  by-products  and  dore 

07 

07 

Superintendence  and  assaying  .  . 

15 

15 

Silver  loss,  actual.  . 

50 

50 

$6.88 

$5.19 

*  Interest  on  power  plant  not  included,  as  this  is  figured  as  part  of  power 
cost. 


Other  items  for  expressage,  management,  taxes,  insurance, 
etc.,  I  assume  to  be  practically  the  same  for  each  process. 
The  above  estimate  applies  to  the  purer  grades  of  bullion,  free 
from  bismuth.  Copper  does  not  average  as  high  as  .8%  in 
many  cases,  but  that  is  usually  the  result  of  skimming  the 
bullion  at  the  smelter,  the  dross  going  back  to  the  lead  fur. 
naces  and  yielding  copper-lead  matte;  but  the  end-result  is 
the  same  whether  the  copper  dross  is  skimmed  by  the  smelter 
or  refiner,  for  the  metallurgical  process  is  the  same  in  each 
case. 

If  bullion  with  more  impurity  is  under  consideration,  the 
relative  advantage  of  the  electrolytic  process  is  greater.  For 
example,  if  the  bullion  contains  say  .05%  of  bismuth,  not  a 
large  or  unusual  amount,  the  electrolytic  process  produces 
corroding  lead,  while  the  zinc  process  does  not,  making  a  fur- 
ther difference  in  this  country,  apart  from  the  value  of  the 
bismuth  saved,  of  $2.00 .to  $2.50  per  ton.  With  higher  anti- 
mony the  advantage  of  the  electrolytic  process  again  increases, 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     277 

the  amount  being  easily  figured  from  the  known  difference  in 
antimony  loss,  10%  and  40%,  and  the  value  of  pure  lead 
and  antimony,  as  against  that  of  the  same  combined  in 
hard  lead. 

The  present  aim  of  lead  smelters  is  to  exclude  from  the 
furnaces  ores  containing  antimony  and  especially  bismuth  in 
order  to  produce  as  pure  bullion  as  possible.  If  the  lead  is 
refined  electrolytically,  these  metals  become  a  source  of  profit, 
and  the  way  is  opened  for  the  utilization  of  low-grade  bismuth 
ores  particularly. 

The  following  table  shows  the  cost  of  the  two  processes 
under  the  head  of  labor,  coal,  chemicals  and  zinc. 


TABLE   100. 


Parkes 

Betts  I 

'rocess. 

Process. 

Steam  Power. 

Gas  Power. 

Labor.      ...                          ... 

$1  41 

$1  89 

$1  89 

Fuel  for  all  purposes  at  $2.50.  ..  . 
Chemicals.  .  .                 

0.75 
0.05 

0.58 
0.66 

0.35 
0.66 

Zinc  

0.96 

This  shows  labor  to  be  less  with  the  Parkes  process,  while 
fuel  and  materials  are  less  for  the  electrolytic  process.  I  have 
assumed  that  the  coal  is  of  good  quality  and  2  Ibs.  are  required 
to  generate  1  E.H.P.  hour  with  steam,  and  1  Ib.  .with  gas 
engines.  The  fuel  for  the  Parkes  process  -includes  the  fuel  for 
treating  by-products  up  to  and  including  fuel  used  in  refining 
copper. 

The  following  estimates  of  cost  of  a  refinery  to  treat  50 
tons  of  bullion  per  day,  with  a  maximum  capacity  of  60  tons, 


278  LEAD  REFINING  BY  ELECTROLYSIS. 

will  serve  as  a  basis  for  other  calculations  under  special  con- 
ditions. 

The  cost  of  construction  is  greatly  different  with  different 
arrangements  of  plant,  cascade  system,  Walker  system  or 
series  system,  and  slime  plant.  The  following  figures  apply 
to  the  Walker  system.  The  most  economical  arrangement  of 
tank  plant  and  melting  plant  I  believe  to  be  is  to  have  the 
two  parts  under  the  same  roof,  in  a  long  building  and  com- 
manded by  the  same  cranes.  The  anodes  can  then  be  taken 
directly  from  the  casting  floor  to  the  tanks  without  rehand- 
ling,  and  the  cathodes,  after  spraying,  can  be  dumped  directly 
from  the  tanks,  in  or  near  the  melting  furnace,  depending  on 
the  kind  of  furnace.  To  save  in  the  number  of  trips  required 
of  the  crane,  which  would  have  to  be  operated  steadily  to  load 
and  unload  as  much  metal  as  60  tons  per  day  from  melting 
floor  to  tanks  and  back,  the  tanks  would  be  made  of  the  largest 
practicable  size,  to  take  6500  amperes,  for  60  tons  production. 
There  would  be  two  cranes  on  the  single  runway,  in  a  building 
55X250  feet,  of  which  100  feet  in  length  would  be  occupied 
by  the  tanks.  The  melting  room  need  not  necessarily  be 
limited  to  the  same  width  as  the  tank  floor. 

The  cathodes  are  assumed  to  be  of  lead-plated  steel,  which 
will  save  enough  in  a  year  in  operating  cost  to  pay  for  them- 
selves. The  current  density  to  be  15  amperes  per  square 
foot  for  50  tons  per  day,  and  18  amperes  for  60  tons  per  day. 
The  current  efficiency  is  assumed  to  be  90%,  and  will  probably 
average  95%  with  steel  cathodes. 

The  power  plant  would  be  required  to  deliver  a  maximum 
of  6500  amperes  and  43  volts  (  =  280  K.W.)  to  the  depositing 
tanks.  If  only  50  tons  per  day  were  produced  197  K.W.  are 
required,  and  for  40  tons  per  day  128  K.W.  The  power  plant, 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     279 

if  in  a  single  unit,  should  be  capable  of  operating  efficiently 
from  less  than  half  its  maximum  capacity,  all  the  way  up. 
The  power  for  treating  slime  and  general  power  and  lighting 
will  be  included  in  the  estimate  later. 


Power  plant  for  lead  depositing  at  $N135  per  K.W $38,000 

104  depositing  tanks  3  feet  wide,  3  feet  10  inches  deep,  8  feet 

6  inches  long  inside 5,200 

200  feet  £  steel  rods.  ... $4.00 

Labor  on  concrete 10 . 00 

Molds  expenses 2 . 00 

3  barrels  cement 4 . 50 

22  cubic  feet  sand 1 . 00 

43  cubic  feet  rock 2 . 40 

375  Ibs.  sulphur 4.70 

Fuel .50 

Paint 1 . 00 

Concrete  piers  and  beams 12 .00 

Labor  coating  tanks 3 . 00 


$45.10 
Wood  tanks  are  more  expensive. 

Lumber,  650  ft.  yellow  pine  at  $35.00 $27 . 50 

Labor,  50  hours 15.00 

Iron,  200  Ibs 8.00 

Paint 1 . 50 

Piers  and  timber  supports 10 . 00 


$62.00 


Electrolyte,  about  7000  cubic  feet 7,000 

70  tons  fluorspar  at  $14.50 $980 

80  tons  sulphuric  acid  at  $15 1,200 

18  tons  fine  quartz  at  $20 360 

20  tons  white  lead  at  $120 2,400 

Labor 1,250 

Repairs 500 

Coal 200 

$6,890 


280  LEAD  REFINING  BY  ELECTROLYSIS. 

For  grading  and  preparing  solution-tight  floor  under  tanks,  on  a 

level  site,  about 1,000 

Tank  part  of  building  55X140  ft.  at  $1.25  per  square  foot  for  walls 

and  roof 9,600 

2  electric  cranes  installed 12,000 

Copper  for  bus  bars  at  25  cents  per  Ib 1,250 

Concrete  electrolytic  storage  tanks 500 

2400  steel  cathodes  £"  thick  at  3  cents 5,400 

Labor  and  material  for  same 1,200 

Pumps,  hose,  cleaning  tanks,  electrode  racks,  starting-sheet  appara- 
ratus,  evaporator,  slime-washing  tanks,  lights,  water  connec- 
tions, tracks,  cars,  sulphur  tank,  total 5,000 

Royalty  for  use  of  Walker  system 

Hydrofluoric-acid  plant.     This  is  quite  cheap  to  instal,  and  may 

be  expected  to  cost  $1,500  or  less  for  a  good-sized  plant 1,500 

Total  for  tank  plant,  exclusive  of  royalty $49,650 


The    cascade    arrangement    would    cost    more,    about    as 
follows : 

For  more  building $3,000 

For  more  copper  at  25  cents 2,275 

For  power  plant  to  supply  power  lost  in  conductors , .      .  1,690 

$6,965 
Melting  plant  costs: 

3  60-ton  kettles  complete  with  stack 3,110 

Cast  iron,  at  3  cents $1,300 

55,000  red  brick,  at  $10 550 

12,000  fire-brick,  at  $30 360 

Mason's  labor 700 

Supplies 100 

Reinforcing  iron 100 

$3,110 

Building,  about  6,000  sq.  ft 8,000 

Molds,  open 275 

Tracks,  cars  and  hoists,  crane  runway,  etc 3yOOO 

$14,385 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     281 

Slime  plant,  to  treat  daily  600  Ibs.  copper,  1,200  Ibs.  antimony, 
400  Ibs.  arsenic,  3,750  ozs.  silver  and  gold,  and  250  Ibs.  lead,  in 
slime,  beside  2  tons  of  copper-lead  matte: 

Slime-dissolving  tanks  for  ferric  solution,  total  capacity  1,000  cu.  ft.  1,200 

Antimony-dissolving  tanks,  150  cu  ft 300 

Lead  filter-press,  with  montejus,  for  slime 600 

Storage  tanks,  lead-lined,  for  sulphate  and  fluoride  solutions,  3,500 

cu.  ft.  capacity 1,500 

18  2,000-amp.  copper-iron  electrolytic  tanks 6,300 

10  2,000-amp.  antimony  tanks  with  cathode^ 1,250 

Crucible  melting  furnaces  for  antimony,  gold,  silver,  dore*,  with 

molds 1,000 

Parting  plant 600 

Building,  about  5,000  sq.  ft.,  at  $1.50  per  sq.  ft 7,500 

Dissolving  tank  for  matte 600 

Filter  press  and  montejus  for  matte 600 

Roasting  furnace 1,000 

Accessory  apparatus 2,000 

Filters  for  antimony  solution 100 

Mill  for  grinding  matte 500 

$25,050 

Power  plant  for  treating  slime,   capacity   120  K.W.,  at  $135. .       16,200 
For  general  purposes,  30  H.P.,  at  $135 4,050 

Total  costs  of  refinery,  maximum  capacity  60  tons  per  day,  would 
then  be: 

Power  plant $58,200 

Tank  plant 49,150 

Meltirig  plant 14,385 

Slime  plant 25,050 

$146,785 
Engineering  expenses,  railroad  facilities,  land,  contingencies  not  included. 

A  series  plant  for  a  maximum  production  of  60  tons  per 
day,  provided  with  a  plant  to  treat  slime  by  the  roasting-with- 
sulphuric-acid  process,  would  work  out  about  as  follows: 

Maximum  current  density  16  amperes  per  square  foot. 
Thickness  of  electrodes  to  be  J  inch,  and  spaced  li  inches  apart. 


282  LEAD  REFINING  BY  ELECTROLYSIS. 

Volts  per  plate  .22,  efficiency  90%.  Anodes  3  feet  square. 
Tanks  4J  feet  deep,  3  feet  2  inches  wide,  and  8  feet  4  inches 
long,  taking  56  plates  and  producing  with  144  amperes,  1,450 
Ibs.  of  lead  per  day,  or  refining  about  1,490  Ibs.  of  bullion. 
88  tanks  arranged  in  11  sets  of  8  tanks  each,  10  sets  always 
in  use,  absorbing  altogether  1,440  amperes  and  100  volts. 

Lead-depositing  power  plant  145  K.W.,  at  $135 $19,600 

88  tanks  of  concrete,  at  $55 $4,840 

Electrolyte,  about  8,000  cu.  ft 8,000 

2  electric  cranes.  .  . 12,000 

Copper  conductors,  2,500  Ibs 625 

Preparing  floor  under  tanks 1,000 

Building,  55-125  feet  at  $1.25  per  sq.  ft 8,500 

Hydrofluoric-acid  plant 1,500 

Electrolyte  storage  tanks 500 

Accessories 5,000 


Tank  room  and  equipment $41,965 

Melting  plant,  using  rolls  to  roll  anodes  or  closed  molds $22,000 

Slime  plant,  using  roasting  with  sulphuric-acid  process: 

Mixer  for  slime  and  H2SO4 $250 

Flat  cars  and  oven  for  drying  slime 2,700 

Electrolyti-c  copper  tanks,  15  for  700  amp 800 

Electrolytic  antimony  tanks,  23  for  700  amp 1,500 

Dissolving  tanks,  with  stirring-gear 800 

Filter  press  and  montejus 600 

Storage  tanks 1,200 

Evaporators  foV  H^O4.  .  . 200 

Crucible  melting  furnaces.    . 1,000 

Parting  plant 600 

Building  about  3,000  sq.  ft.,  at  $1.50 4,500 

Accessories 2,000 


Total $16,150 

Power  for  slime  treatment,    75  K.W. 
"     and  lights,  30  K.W. 

105  K.W.  at  $135 $14,200 


REFINERY  CONSTRUCTION,  OPERATION,  REFINING  COSTS.     283 

For  a  comparison  between  the  two  methods  of  installation 
we  have  for  plants  with  60  tons  maximum  capacity: 


TABLE  101. 

Power  plants $  58,200  $  33,800 

Tank  plants 49,150  41,965 

Melting  plants 14,385  22,000 

Slime  plants 24,050  16,150 

$145,785  $113,915 


Allowing  for  land,  engineering  expenses,  shipping  facilities, 
etc.,  total  cost  may  be  taken  at  $2,000  to  $3,000  per  daily 
ton  capacity.  The  above  figures  are  only  intended  to  serve 
as  a  basis  for  computations,  and  not  to  furnish  exact  infor- 
mation, which  it  is  impossible  to  do  anyway  as  costs  are  sub- 
ject to  great  variations,  so  in  many  cases  I  have  not  thought 
it  worth  while  to  try  to  ascertain  exact  costs  of  different 
apparatus. 


CHAPTER  VIII. 


PRODUCTS. 

THE  analyses  of  refined  lead,  presented  as  tables,  are  col- 
lected from  numerous  sources,  and  are  not  selected  in  any 
way,  but  include  all  the  analyses  I  have.  The  Consolidated 
Mining  and  Smelting  Company  of  Canada,  Ltd.,  have  kindly 
given  me  the  average  analyses  of  their  electrolytic  lead  and 
lead  bullion,  which  is  given  as  Table  102. 


TABLE   102. 
BULLION. 

Au 

Ag 

Cu 

Fe 

Sb 

1904  averages  
1905        '  '       

1  .  50  ozs. 
1.00    " 

200      ozs 
109.1    " 

>.       .50^ 
.19$ 

209 

-) 

0 

\ 

0 
' 

0 

.07% 
.05% 

.55% 
.44% 
.81% 
.75% 

1906        '  '       

1907        "         so  far  

209 

Sn 

As 

Mn 

Zn 

Bi 

1904  averages.  .  . 

Trace 

<  i 

None 
Trace 

•11% 

.23% 
.15% 

.25% 

Trace 

(  « 

(  S 

Trace 

<  « 

None 

1905        " 

1906        "       
1907        "         so  far  

TABLE   103. 
PIG  LEAD. 

Silver 

Cu 

Fe 

Sb 

Sn 

Bi 

As 

Ni 

Co 

Averages.  .  . 

.52  ozs. 

.0006% 

.0007% 

.0006% 

None 

None 

None 

None 

None 

284 


PRODUCTS. 


285 


The  silver  is  unusually  high  in  the  Trail  lead,  but  with 
other  bullion  it  has  probably  averaged  about  J  ounce.  By 
further  washing,  the  silver  may  be  largely  reduced,  but  they 
find  it  does  not  pay  to  save  it.* 

The  United  States  Metals  Refining  Company,  at  their  plant 
at  Grasselli,  produce  lead  of  about  the  following  composition :  f 

TABLE   104. 


Ag 

Cu 

Sb 

Bi 

Fe 

As 

Pb 

.  00070% 
=  .21  ozs. 

.00100% 

.00096% 

.00070 

.00140% 

Trace 

99.99524% 

The  quality  of  the  lead  varies  with  the  skill  and  ex- 
perience of  the  workmen  in  drawing  cathodes  and  washing 
them.  An  inexperienced  man  is  apt  to  wipe  off  slime  from 
the  anodes  on  the  cathodes  in  drawing  the  latter.  The  fol- 
lowing data  from  Trail,  1902,  illustrates  this: 

TABLE   105. 


Cast. 

Oz.  Ag 
in  Lead. 

Cast. 

Oz.  Ag 

in  Leavl. 

Cast. 

Oz.  Ag 
in  Lead. 

Aug.  17  
19  
21        .    . 

0.48 
0.35 
0.26 

Sept.    22 
24 
26 

0.43 
0.35 
0.18 

Oct.    28 
30 

0.24 
0.23 

23  
25  
27  

0.17 
0.14 
0.26 

27 
29 

0.30 
0.32 

Nov.    3 
5 

7 

0.38 
0.34 
0.38 

27  
29   . 

0.25 
0  20 

Oct.       1 
3 

0.14 
0.15 

10 
13 

0.34 
0  35 

31  

0.32 

4 

0.13 

15 

0  24 

Sept.    2  
4  

0.28 
0.19 

6 
8 
10 

0.22 
0.17 
0.17 

19 
19 
23 

0.22 
0.23 
0.20 

7 

0  25 

13 

0.16 

25 

0  18 

8 

0  24 

15 

0.15 

28 

0  21 

10.  .    .    . 

0.28 

16 

0.10 

28 

0.22 

12  
15  
16  

10 

0.29 
0.43 

0.45 
Ooq 

18 
20 
22 

OK 

0.16 
0.15 
0.11 
01  4 

Dec.     1 
1 

0.19 
0.12 

20  

0.40 

27 

0.26 

Average 

0  25 

*  Communicated  by  the  Company.         f  Ditto. 


286 


LEAD  REFINING  BY  ELECTROLYSIS. 


The  bullion  averaged  310.4  ozs.  Ag,  and  3.15  ozs.  Au.  The 
increase  in  silver  about  October  27th  and  November  3d  was 
caused  by  putting  on  new  men  at  drawing  and  washing  cath- 
odes, who  gradually  became  accustomed  to  the  work,  with  a 
consequent  slow  reduction  in  the  silver  figures. 

As  showing  the  unequal  distribution  of  silver  in  the  cath- 
odes, the  following  data  by  Dr.  E.  F.  Kern  are  interesting: 


TABLE   106. 


Ag. 


Rough  sample  from  center  of  steel  cathode 97  ozs. 

Sample  from  edge  of  same  rough  sheet 1 . 64 

Large  warts  of  lead  on  steel  cathode 2 . 44 

Smoother  cathode  from  same  tank 0 . 23 

Smooth  and  bright  cathode 0 . 04 

Smooth  heavy  cathode 0 . 09 

Smooth  deposit  on  steel  cathode 0 . 07 

TABLE  107. 
ANALYSES  OF  REFINED  LEAD.     TRAIL,  1902. 


No. 

Cu, 
Per  Cent. 

As, 
Per  Cent. 

Sb, 
Per  Cent. 

Fe, 
Per  Cent. 

Zn, 

PerCent 

Sn, 
Per  Cent. 

AgOz- 
P.T. 

Ni.Co.Cd 
PerCent. 

Bi 
PerCent 

1 
2 

Q 

0.0006 
0.0003 
0  0009 

0.0008 
0.0002 
0  0001 

0.0005 
0.0010 
0  0009 

0.0010 
0  0008 

None 

<  i 

0  24 

4 

0  0016 

0  0014 

0  47 

None 

5 

0  0003 

0  0060 

0  0003 

0  22 

<; 

0  0020 

0  0010 

0  0046 

0  22 

None 

7 
8 

0.0004 
0.0004 

None 

0.0066 
0.0038 

0.0013 
0.0004 

None 

0.0035 
0.0035 

0.14 
0.25 

9 
10 
11 
12 
13 
14 
15 
16 
17 

0.0005 
0.0003 
0.0003 
0.0005 
0.0005 
0.0004 
0.0003 
0.0006 
0  0006 

None 

0.0052 
0.0060 
0.0042 
0.0055 
0.0055 
0.0063 
0.0072 
0.0062 
0  0072 

0.0004 
0.0003 
0.0013 
0.0009 
0.0007 
0.0005 
0.0003 
0.0012 
0  0011 

0.0039 
0.0049 
0.0059 
0.0049 
0.0091 
0.0012 
0.0024 
0.0083 
0  0080 

0.28 
0.43 
0.32 
0.22 
0.11 
0.14 
0.24 
0.22 
0  23 

18 
19 

0.0006 
0  0005 

0.0057 
0  0066 

0.0010 
0  0016 

0.0053 
0.0140 

0.34 
0.38 

19 

0  0005 

0  0044 

0.0011 

0.0108 

0.35 

20 

0  0004 

0  0047 

0  0015 

0  0072 

0  22 

20 

0  0004 

0  0034 

0  0016 

Trace 

0  23 

21 

0.0022 

0.0010 

0.0046 

None 

0.0081 

0.38 

None 

None 

PRODUCTS. 

TABLE   108. 

ANALYSES  or  REFINED  LEAD.     TRAIL,  1903  OR  1904. 


287 


Silver, 
Per  Cent. 

Copper, 
Per  Cent 

Lead, 
Per  Cent. 

Iron, 
Per  Cent. 

Antimony, 
Per  Cent. 

Tin, 
Per  Cent 

Bi.Co.Ni, 

00129 

0015 

0015 

0148 

Nil 

.00129 

.0005 

99.996 

.0015 

.0006 

Trace 

.0015 

.0011 

99.976 

.0015 

.0003 

' 

.00030 

.0014 

99.995 

.0015 

.0006 

' 

.00192 

.0005 

99.995 

.0017 

.0003 

i 

.00077 

.0010 

99.997 

.0013 

Trace 

t 

.00084 

.0020 

99.995 

.0015 

.0003 

1 

.00091 

.0007 

99.996 

.0015 

.0009 

i 

TABLE  109. 

ANALYSES  OF  REFINED  LEAD.     TRAIL,  1904. 
Letter  from  Mr.  W.  H.  Aldridge. 


Silver,  Per  Cent. 

Copper, 
PerCent 

Lead, 
Per  Cent. 

Iron, 
PerCent 

Tin, 
PerCent 

Anti- 
mony. 
Per  Cent. 

Arsenic, 
PerCent 

Bi, 

PerCent 

Zinc, 
PerCent 

.0013  =.38  ozs. 

.00075 

99.9938 

.00075 

.0001 

.0028 

None 

None 

.0005 

.0017=.  50    " 

.001 

99.9930 

.0012 

.0001 

.0026 

" 

<  < 

.0004 

.0019=.  55    " 

.0009 

99.9943 

.0007 

.0001 

.0017 

i  ( 

.0004 

TABLE  110. 

ANALYSES  OF  BULLION.     TRAIL,  1902. 


No. 

Fe, 
PerCent 

Cu, 
PerCent 

Sb, 
PerCent 

Sn, 
PerCent 

As, 
PerCent 

PerCent 

Au, 
PerCent 

Pb, 
PerCent 

AgOz. 
P.T. 

AuOa 
P.T. 

1 

0.0075 

0.1700 

0.5400 

0.0118 

0.1460 

1.0962 

0.0085 

98.0200 

319.7 

2.49 

2 

0.0115 

0.1500 

0.6100 

0.0158 

0.0960 

1.2014 

0.0086 

97.9068 

350.4 

2.52 

3 

0.0070 

0.1600 

0.4000 

0.0474 

0.1330 

1.0738 

0.0123 

98.1665 

313.2 

3.6 

4 

0.0165 

0.1400 

0.7000 

0.0236 

0.3120 

0.8914 

0.0151 

97.9014 

260.0 

4.42 

5 

0.0120 

0.1400 

0.8700 

0.0432 

0.2260 

0.6082 

0.0124 

98.0082 

177.4 

3.63 

6 

0.0055 

0  .  1300 

0.7300 

0.0316 

0.1030 

0.6600 

0.0106 

98.2693 

192.5 

3.10 

7 

0.0380 

0.3600 

0.4030 



Trace 

0.7230 

0.0180 

98.4580 

210.9 

5.25 

288 


LEAD  REFINING   BY  ELECTROLYSIS. 


TABLE  111. 

SLIME  ANALYSES. 


No. 

Anodes  . 

Cu, 
PerCent 

PerCent 

Sb, 
PerCent 

As, 
PerCt. 

Pb, 
PerCt. 

1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 

Lead  Trail  B  C 

8.83 
22.36 
1.90 
9.30 
6.38 
1.40 
6.60 
12.56 
7.10 
7.70 
8.1 
7.82 
41 
18 
57 
53.29 

28.15 
23.05 
32.11 
4.7 
3.90 
31.62 
32.21 
78.45 
29.  2Q 
31.90 
14.6 
2.44 
24 
51.4 
14.80 
12.90 

27.10 
21.16 
29.51 
25.32 
50.16 
35.71 
24.60 
4.12 
30.50 
37.60 
27.6 
75.34 

2.00 
3.30 

12.42 
5.40 
9.14 
44.58 
15.23 
4.91 
2.20 

17.05 
10.62 
9.05 
10.30 
5.30 
9.57 
12.60 
3.00 
10.20 
12.60 
16.0 
12.23 

5.26 
Tr. 

Lead,  Trail,  B.  C. 

Lead,  Monterey,  Mexico  

Lead,  Mexican  

Lead  Mexican 

Lead  Trail   B  C 

Lead  Trail,  B  C 

Rich  lead,  Parkes  process  

Lead,  Trail,  B.  C                

6.10 
2.80 
7.0 
0.24 

2.60 
1.15 

Lead,  Trail,  B.  C  

Lead,  Trail,  B.  C  

Lead  from  El  Doctor  Mine,  Mexico.  .  .  . 
Copper,  Montana  converter  anodes.  .  .  . 
Copper,  Montana  reverberatory  anodes 
Copper  Boston  and  Montana 

Copper  Boston  and  Montana 

Uo. 

Anodes. 

Bi, 
PerCt. 

s. 

PerCt. 

Fe, 

PrCt. 

1.27 
1.12 
.49 

Nil 

Oz.  Au. 

Se, 
PrCr. 

Te, 
PrCt. 

1 
2 
3 
4 
,5 
€ 
7 
8 
9 
10 
11 
12 
13 
14 
15 
16 

Lead,  Trail,  B.  C  

Nil 
Nil 
Tr. 

29.1 

180.33 
81.99 

34.5 

18 
38 

2.0 

.26 

1.00 

1.97 

Lead,  Trail,  B.  C.  .  .  .  
Lead  Monterey,  Mexico  ... 

Lead  Mexican  . 

.52 

19.74 

Nil 

Lead  Mexican.  .                 

Lead,  Trail,  B.  C.             

Lead,  Trail,  B.  C  

Rich  lead  Parkes  process 

.88 

0.81 
1.95 

1.35 

Lead  Trail  B  C 

Lead  Trail,  B  C. 

Lead  Trail,  B  C. 

Lead  from  El  Doctor  Mine,  Mexico.  .  . 
Copper  Montana  converter  anodes 

Copper,  Montana  reverberatory  anodes 
Copper,  Boston  and  Montana  
Copper  Boston  and  Montana  

5.70 
1.55 

ii!96 



REMARKS. — 1,  2.  Trans.  Am.  Inst.  Min.  Eng.,  1904,  p.  182.  3,  4.  Trans.  Am. 
Unst.  Min.  Eng.,  1904,  p.  183.  5.  Original.  6,  7.  Mines  and  Minerals,  Vol.  25 
•<1905),  p.  288.  8,  9,  10,  11,  12.  Original.  13,  14.  Trans.  Am.  Inst.  Min.  Eng., 
1904,  p.  310.  15,  16.  Original. 


PRODUCTS. 


289 


TABLE   112. 
ANALYSES  OF  BULLION  AND  REFINED  LEAD.     TROY,  N.  Y. 


Ag, 
Per  Cent. 

Cu, 
Per  Cent. 

Sb, 
IPer  Cent. 

Pb, 

Per  Cent. 

Bullion 

0  50 

0  31 

0  43 

98  76 

Refined  lead 

0  0003 

0  0007 

0  0019 

99  9971 

TABLE  113. 

ANALYSES  OF  BULLION  AND  REFINED  LEAD.     TROY,  N.  Y. 


Cu 

PerCent 

Bi 

PerCent 

As 
PerCent 

Sb 
PerCent 

AgOz. 
P.T. 

PerCent 

AuOz. 
P.T. 

Fe 
PerCent 

Zn 
PerCent 

Bullion  
Refined  lead.  . 

0.75 
0.0027 

1.22 
.0037 

0.936 
0.0025 

0.6832 
0.0000 

358.89 

1.71 
None 

0.0022 

0.0018 

0.0010 

TABLE   114. 
ANALYSES  OF  BULLION,  REFINED  LEAD  AND  SLIMES.     TROY,  N.  Y. 


Pb 

PrCt. 

Cu 
PerCent 

As 
Per  Cent. 

Sb 
Per  Cent. 

Ag  Oz. 
Per  T. 

Per  Cent. 

Fe,  Zii, 
Ni  Co, 
PrCt. 

Bi 

Bullion.  . 

96.73 

0.096 

0  0013 

0.85 
0.00506 

9.14 

1.42 
0.0028 

29.51 

about  275 
9366.9 

0.00068 

0.0027 
0.49 

Tr. 

t  ( 

Refined  lead.  .  . 

Slimes       (dry 
sample)   . 

9.05 

1.9 

TABLE   115. 

ANALYSES  OF  BULLION,  REFINED  LEAD  AND  SLIMES.     TROY,  N.  Y. 


Pb 
Per  Cent. 

Cu 
Per  Cent. 

Bi 
Per  Cent. 

Ag 
Per  Cent. 

Sb 
Per  Cent. 

As 
Per  Cent. 

Bullion.  . 

87  14 

1   40 

0  14 

0  64 

4  0 

7   4 

Lead.  .    . 

0  0010 

0  0022 

0  0017 

Trnpp 

Slimes  

10.3 

9.3 

.  0.52 

4.7 

25.32 

44.58 

290 


LEAD  REFINING  BY  ELECTROLYSIS. 


The  following  analyses  by  the  Osaka  Technical  Analyzing 
Department,  presumably  of  lead  in  the  Japanese  market,  prob- 
ably give  a  good  idea  of  the  present  quality  of  commercial 
lead  in  the  world's  markets: 


TABLE  116. 
PIG  LEAD  ANALYSES. 
By  the  Osaka  Technical  Analyzing  Department. 


Per  Cent. 

Selby. 

Trail. 

Smelter. 

English 
Chemical  . 

B  H.P 

Enthoven 

Lead  .             

99.9579 

99.9890 

99.9762 

99.9693 

99  .  9853 

99.9851 

Insolubles  

0.0040 

Trace 

Trace 

Trace 

Trace 

Trace 

Bismuth  

0.0300 

None 

0.0046 

<  ( 

None 

0.0048 

Cadium 

Trace 

0  0002 

0  0007 

Trace 

Trace 

Nickel     . 

0  0001 

Trace 

Trace 

0.0003 

None 

<  < 

Cobalt  

None 

None 

<  i 

Trace 

Trace 

1  1 

Silver               .    ... 

0.0010 

0.0025 

1  1 

0.0020 

0.0009 

0.0015 

Manganese  

0.0008 

None 

0.0003 

None 

None 

None 

Copper  
Antimony  

None 

1  1 

0.0003 
None 

None 
0.0137 

0.0097 
0.0149 

0.0108 

(  ( 
0.0160 

Tin 

0  0004 

0  0007 

None 

None 

0  0004 

None 

Arsenic  
Zinc.  .               

0.0024 
0.0003 

0.0020 
0.0002 

0.0090 
Trace 

0.0002 
Trace 

None 
0  0001 

1  1 
Trace 

Iron  

0.0027 

0.0053 

0.0039 

0.0029 

0.0025 

0.0026 

NOTE. — Selby  and  Smelter  are  American;    Trail,  Canadian;    Enthoven 
and  Chemical,  English;  B.  H.  P.,  Australian. 


CHAPTER  IX. 
TREATMENT  OF  LEAD  CONTAINING  BY-PRODUCTS. 

THE  refining  of  copper-lead  alloys  with  high  copper  is 
of  some  importance.  First,  because  such  alloys  can  be  pro- 
duced as  "bottoms"  from  copper-lead  matte,  and  a  method 
of  saving  both  lead  and  copper  is  then  provided.  Second, 
because  some  lead  bullions  give  a  good  deal  of  dross  in  remelt- 
ing  which  can  not  very  well  be  stirred  into  the  lead  to  make  a 
uniform  anode,  and  the  natural  method  of  treating  such 
drosses,  containing  as  they  do  from  80%  to  90%  lead  or  more, 
is  to  get  them  into  some  kind  of  an  anode  and  extract  the 
lead  electrolytically  in  the  usual  manner. 

Dr.  E.  F.  Kern  tested  many  methods  of  treatment  in  my 
laboratory  using  an  alloy  of  60%  Pb,  39%  Cu,  and  1%  Ag, 
which  methods  included  removing  of  the  lead  by  the  com- 
bined action  of  fluosilicic-acid  solution  and  air,  the  alloy  losing 
2%  in  twenty-one  hours.  The  alloy  was  also  ground  up, 
mixed  with  broken  electrolytic  lead  peroxide,  and  let  stand 
three  and  one-half  days  with  solution  containing  lead  fluo- 
silicate  and  fluosilicic  acid.  At  the  end  of  that  time  all  the 
lead  had  dissolved  out,  as  well  as  some  copper,  leaving  a 
porous  copper  material  of  the  same  shape  as  the  original 
pieces  of  alloy.  Some  Pb02  remained,  the  execution  of  the 
experiment  being  faulty  in  not  using  the  right  amount  of 

291 


292  LEAD  REFINING  BY  ELECTROLYSIS. 

Pb02  to  either  dissolve  the  lead  alone,  or  both  the  lead  and 
copper. 

The  chemical  reactions  are: 

Cu  +  Pb02  +  2H2SiF6  =  PbSiF6  +  CuSiF6  +  2H20 
Pb+Pb02  +  2H  SiF6=2PbSiF6 


This  method  would  not  be  a  promising  one,  although  the 
lead,  or  lead  and  copper  dissolved,  as  well  as  the  lead  peroxide 
and  the  fluosilicic  acid,  could  be  recovered  by  electrolyzing 
the  solution  with  metal  cathode  and  carbon  anodes.  When 
this  is  done,  lead  peroxide  deposits  on  the  anodes  as  a  hard, 
greenish  black,  lustrous,  well-conducting  deposit  of  a  smooth- 
ness superior  to  most  metallic  deposits.  The  reactions  are 
the  reverse  of  those  just  given.  The  electromotive  force  when 
depositing  lead  is  about  2.1  volts,  and  1.7  volts  when  deposit- 
ing copper. 

The  alloy,  or  a  very  similar  one,  was  also  treated  with  a 
solution  of  ferric  fluosilicate  which  dissolved  out  the  lead, 
and  also  traces  of  copper,  from  using  a  little  too  much  ferric 
salt.  The  residue  retained  the  original  shape  of  the  alloy, 
but  was  very  soft  and  porous,  consisting  of  copper  and  silver. 
In  this  process  the  solution  was  to  be  electrolyzed  for  the 
lead  and  recovery  of  the  ferric  fluosilicate. 

Far  the  best  method  consists  in  treating  the  alloy  as  anode 
in  the  usual  lead-depositing  solution,  with  a  somewhat  smaller 
current  density. 

In  one  experiment  the  following  data  were  noted:  Cur- 
rent density  about  12.5  amperes  per  square  foot.  Distance 
between  electrodes  1  to  2  inches.  Volts  about  .15  to  .20,  rising 
later  to  .42  volts,  when  slime  had  to  be  removed.  Solution 


TREATMENT   OF   LEAD   CONTAINING   BY-PRODUCTS.      293 

4%  Pb,  15%  SiF6.  The  anode  was  1  inch  thick  and  the  slime 
had  to  be  removed  several  times  before  the  anode  was  com- 
pletely decomposed. 

TABLE  117. 

Weight  anode 1778  gr. 

Lead  deposited 732  gr. 

Slime 340  gr. 

Alloy  remaining 675  gr. 

Dr.  Kern  put  85  gr.  of  the  slime  in  a  small  lead  box 
with  perforations  in  the  sides,  and  electrolyzed  it  with  a  solu- 
tion containing  20%  CuS04-5H20  and  5%  H2S04,  with  cop- 
per cathodes. 

As  the  slime  settled  down  50  gr.  more  were  added, 
making  135  gr.  used  altogether.  Electromotive  force  .2  volts; 
copper  deposited  100  gr.;  weight  of  residue  of  silver  and 
lead  sulphate  37  gr. 

Analysis  of  these  figures  indicates  the  following:  135  gr. 
slime  result  from  about  475  gr.  of  the  alloy.  The  slime  con- 
tains then  4  gr.  silver  and  33  gr.  lead  sulphate,  per- 
haps a  little  of  this  coming  from  the  lead  box  which  lost  a 
little  in  weight.  As  a  result,  practically  all  the  copper  was 
recovered,  but  8.8%  of  the  lead  was  apparently  converted  into 
lead  sulphate.  Perhaps  some  of  this  apparent  loss  was  due 
to  insufficient  washing  of  the  slime. 

In  the  aggregate  the  quantity  of  copper  dross  converted  into 
matte  by  resmelting,  must  be  quite  large,  and  the  lead  lost 
in  the  final  conversion  of  the  copper-lead  matte  is  well  worth 
saving.  Refiners  could  very  well  treat  their  drosses  by 

• 

casting    into    anodes  at  a  red    heat  and   extracting   the  lead 
electrolytically. 

Experiments  on  refining  hard  lead  with  18.8%  Sb,   and 


294 


LEAD   REFINING   BY   ELECTROLYSIS. 


rich  lead  from  the  Parkes  or  Pattinson  processes,  are  described 
in  Chapter  I.  The  antimony  slime  could  be  refined  direct 
with  the  antimony  fluoride  solution,  as  it  retains  consider- 
able mechanical  strength,  or  it  could  be  ca.st  into  anodes. 

The  electrolytic  lead  process  ought  to  be  of  advantage  in 
a  small  way  in  some  other  branches,  as  for  instance  refining 
the  lead-gold  bullion  produced  in  cyanide  mills. 

Experiments  on  galena  direct  have  been  fruitless. 

Electrolytic  refining  of  lead  bullion  high  in  bismuth,  is 
practiced  on  a  small  scale,  primarily  to  produce  bismuth. 

Table  118  gives  the  composition  of  various  alloys  which 
have  been  successfully  refined,  producing  pure  lead  at  the 
cathodes.  Table  25,  on  page  68,  gives  a  number  of  others 
refined  by  Senn.* 

TABLE  118. 
ANALYSES  OF  LEAD  ANODES. 


Pb 

Cu 

Sb 

As 

Ag 

Bi 

Current  Density 
Per  Sq.  Foot. 

Slime 
Contains. 

88.     % 

1.53% 

.5  % 

9.75% 

1.11% 

7  amps. 

82  37% 

2  22% 

77% 

14  60% 

19% 

7 

65  37% 

19  51% 

5  85% 

1  95% 

7.32% 

2  0 

5  3%  Pb 

65.56% 
82.79% 
88.52% 
60       % 

1.94% 
.97% 
.68% 
39  0% 

18.24% 
9.12% 
6.08% 

5.47% 
2.73% 

1.94% 
.97% 
.68% 
1.0  % 

6.94% 
3.42% 
2.28% 

2.0 
2.0 
2.0 

4-  7 

87.14% 

1.40% 

4.10% 

7.40% 

.64% 

0.14% 

11.6-17 

10.3% 

*  Zeitschrift.  f  iir  Elektrochemie.     1905.     Vol.  XL,  page  229. 


CHAPTER  X. 
ANALYTICAL  METHODS  AND  EXPERIMENTAL  WORK. 

Slime. — Dissolve  1  gr.  in  HC1  and  KC103,  boil  out  chlo- 
rine, add  a  little  water,  neutralize  with  dry  sodium  carbonate, 
add  excess  of  Na2S  solution  (prepared  from  caustic  soda  by 
saturating  with  H2S,  then  adding  another  portion  of  caustic 
soda  of  same  amount,  and  allowing  to  settle  before  using). 
Heat  on  plate  for  an  hour  or  so,  filter,  add  2  to  3  gr.  pure 
caustic  soda  or  potash,  and  determine  Sb  electrolytically. 

The  following  remarks  will  be  useful  in  making  electro- 
lytic antimony  determinations.  If  you  are  using  a  smooth 
platinum  cathode,  deposit  on  it  a  layer  of  antimony  from  a 
fairly  strong  solution  of  tartar  emetic  to  which  a  little  nitric 
acid  has  been  added,  and  the  precipitated  Sb203  redissolvcd  by 
adding  tartaric  acid.  Use  a  current  of  about  1  to  2  amperes 
per  square  foot  in  preparing  the  cathode,  which  is  then  washed 
with  water,  dried  and  weighed. 

The  antimony  deposits  from  the  sulphide  solution  made 
as  above  0:1  the  prepared  cathode  in  a  beautiful,  smooth  con- 
dition fit  for  accurate  determinations.  I  usually  start  the 
electrolysis  cold  with  a  current  of  J  ampere  for  a  cathode 
having  20  square  inches  of  surface,  and  heat  the  solution  up 
while  the  current  is  on  to  70°  and  increase  the  current  to  1J 
to  2  amperes.  After  about  three  hours  turn  off  the  heat,  and 
after  cooling  remove  cathode,  plunge  into  distilled  water  with- 

295 


296  LEAD   REFINING  BY  ELECTRLOYSIS. 

out  interrupting  the  current,  wash,  dry,  and  weigh.  The 
use  of  alcohol  in  drying  is  of  no  advantage,  as  the  antimony 
does  not  oxidize  very  readily  anyway.  I  have  found  the  same 
weight  either  way. 

Add  dilute  H2S04  to  filtrate,  heat,  filter  off  As2S3  +  S,  add 
fairly  dry  paper  and  precipitate  to  about  40  cc.  concentrated 
HN04,  and  digest  gently  on  plate  for  six  to  eight  hours  while 
acid  is  slowly  driven  off.  This  removes  small  amounts  of 
chlorine  and  all  paper.  Determine  As  by  Pearce's  silver  arse- 
nate  method,  described  in  numerous  books. 

For  copper,  silver,  bismuth,  iron,  and  lead  I  have  taken 
a  separate  sample,  dissolved  in  nitric  and  tartaric  acids,  neu- 
tralized with  soda,  added  Na2S  digested  and  filtered.  Pos- 
sibly the  solution  running  through  is  equally  suitable  for  deter- 
mining arsenic  and  antimony,  though  several  failures,  per- 
haps due  to  other  reasons,  have  always  prevented  successful 
results  so  far. 

The  insoluble  sulphides  with  the  filter  paper  are  dried 
placed  in  a  small  beaker,  a  light  applied,  when  the  paper  burns 
off  and  carbonizes.  Concentrated  H2S04  is  added  and  gently 
boiled,  cover  on,  till  carbon  is  all  gone  and  solution  is  clear 
greenish.  Possibly  sodium  or  potassium  bisulphate  would 
work  quicker. 

After  cooling  add  water  and  pass  H2S.  Filter  off  iron, 
determine  it  by  boiling  H2S  from  filtrate,  and  titrating  with 
permanganate.  Redissolve  sulphides  in  H2S04  in  same  way 
again.  Then  neutralize  with  soda  and  add  KCN  free  from 
sulphide.  Pb  and  Bi  remain  insoluble  as  carbonates,  while 
silver  and  copper  dissolve. 

The  silver  and  copper  cyanide  solution,  may  be  acidified, 
AgCN  filtered  off,  and  copper  determined  electrolytically.  I 


ANALYTICAL  METHODS  AND   EXPERIMENTAL  WORK.     297 

have,  however,  got  good  results  by  electrolyzing  the  solution 
for  silver,  using  a  single  dry  battery,  giving  1.3  volts  about 
as  a  maximum,  for  source  of  current.  Time  required  about 
four  or  five  hours,  if  solution  is  warm.  Then  acidify  solution 
with  nitric  acid  under  the  hood,  evaporate  down,  to  remove 
the  HCN  and  determine  copper  electrolytically.  Copper  and 
silver  can  also  be  determined  separately,  the  first  by  dissolving 
1  gr.  of  the  slime  in  nitric  acid,  removing  silver  as  chloride, 
precipitating  with  ammonia,  filtering  and  titrating  with  KCN, 
while  silver  will  often  be  determined  in  a  works  by  assay. 

The  bismuth  and  lead  carbonates  obtained  as  above  are 
dissolved  in  dilute  nitric  acid,  the  solution  is  almost  neutra- 
lized with  ammonia,  heated,  and  a  few  drops  of  HC1  added 
to  throw  out  BiOCl  (Ledoux's  method  *) ,  which  can  be  dried 
and  weighed  at  100°  in  a  Gooch  crucible.  A  convenient  and 
satisfactory  filter  for  a  Gooch  crucible  consists  of  a  small  disc 
of  filter-paper,  the  same  size  as  the  bottom  of  the  crucible. 

Add  sulphuric  acid  to  the  filtrate  from  BiOCl,  and  evap- 
orate for  lead  sulphate,  which  may  be  determined  in  several 
familiar  ways. 

The  analysis  of  metallic  antimony  can  be  made  in  the  same 
way  as  the  analysis  of  slime  given  above,  omitting  the  separa- 
tion and  determination  of  elements  known  to  be  absent. 

Assay  of  dore  bullion.  —  The  method  in  general  use  in 
the  refineries  and  assay  offices  of  this  country  is  about  as 
follows:  The  determination  of  silver  is  carried  out  by  Gay- 
Lussac's  method  of  precipitation  with  salt,  although  Vol- 
hard's  method,  using  a  standard  solution  of  thiocyanate,  gives 
good  results  unless  there  is  considerable  copper  present. 

*  Low,  "Technical  Methods  of  Ore  Analysis,"  page  55. 


298  LEAD  REFINING  BY  ELECTROLYSIS. 

Gold. — 5  gr.  are  digested  in  a  porcelain  crucible  about  2  to 
2J  inches  high,  with  one  to  six  nitric  acid,  until  solution  ceases. 
The  solution  is  decanted,  nitric  acid  one  to  ^one  added,  and 
boiling  continued  until  gold  changes  color.  It  is  then  washed 
with  hot  water  several  times,  dried  and  weighed.  I  under- 
stand at  the  San  Francisco  mint  400  parts  of  gold  are  added 
to  the  assay  for  gold,  and  a  check  made  up  containing  400 
parts  of  gold.  This  is  then  cupelled  with  lead  and  parted  with 
acid  and  weighed,  and  the  surcharge,  or  silver  remaining  in 
the  gold,  determined  from  the  check. 

To  determine  gold  accurately  a  proof  should  be  run,  using 
a  made-up  alloy  containing  gold,  silver,  and  copper,  in  about 
the  same  proportions  as  known  to  exist  in  the  dore,  cupelling 
with  an  equal  amount  of  lead,  and  parting  the  button  and 
weighing  the  gold  in  the  same  manner.  This  is  done  at  the 
Philadelphia  mint. 

Sampling  dore  bullion  may  be  done  by  melting  in  a  graphite 
crucible,  stirring  well,  pouring  off;  after  one-third  and  two- 
thirds  are  about  poured  off,  collect  a  small  sample  by  putting 
small  crucibles  in  stream  of  metal.  Both  samples  are  granu- 
lated separately  and  assayed  separately.  If  they  do  not  agree 
the  bar  is  melted  over  again.* 

Analysis  of  refined  lead.^Five  hundred  gr.  of  lead  are 
cleaned  and  hammered  or  rolled  into  thin  plates,  being  very 
careful  to  use  a  perfectly  clean  and  bright  hammer  and  anvil 
to  avoid  introducing  iron  into  the  sample.  The  lead  is  dis- 
solved in  a  large  beaker  on  the  hot  plate,  in  500  cc.  nitric  acid 
1.42  and  1,000  cc.  water.  If  the  solution  gets  too  hot  it  will 
foam  very  much  and  run  over,  so  that  it  is  necessary  to  watch 

*  Selby  Smelting  and  Lead  Company. 


ANALYTICAL  METHODS  AND  EXPERIMENTAL  WORK.  299 

It  until  most  of  the  lead  is  dissolved.  For  the  same  reason  roll- 
ing or  hammering  the  lead  into  very  thin  strips  is  not  desirable. 

After  all  the  lead  is  dissolved  the  solution  is  generally  per- 
fectly clear,  although  if  more  than  .02-.03%  of  antimony  or 
any  tin  is  present,  it  will  show  some  turbidity.*  The  solu- 
tion should  be  diluted  to  nearly  2  litres  to  prevent  lead  nitrate 
crystallizing  out  on  cooling.  If  mot  perfectly  clear  it  is  fil- 
tered into  a  2-litre  measuring  flask,  otherwise  it  is  merely 
transferred  thereto.  145  cc.  concentrated  sulphric  acid,  pre- 
viously diluted  with  water,  are  added,  and  the  flask  filled  to 
the  mark.  After  settling  1,700  cc.  of  clear  solution  are  secured 
by  pouring  through  a  large  filter.  100  gr.  of  lead  as  sulphate 
occupy  23  cc.,  so  that  we  have  in  solution  -}f-§-£  of  the  impuri- 
ties in  500  gr.  of  lead  =  451  gr.  lead. 

The  1,700  cc.  are  evaporated '  to  fumes  of  H2S04,  taken  up 
with  50  cc.  water,  and  the  lead  sulphate  filtered  off.  The 
lead  sulphate  is  digested  with  pure  sodium  sulphide  solution, 
filtered  and  added  with  the  other  sodium  sulphide  solution 
obtained  further  on.  The  filtrate  from  the  lead  sulphate  is 
treated  hot  with  H2S  for  some  time  and  the  gas  passed 
through  until  cold.  After  settling  completely  it  is  filtered, 
and  iron  and  zinc  determined  in  the  filtrate,  while  the  sulphides 
are  treated  with  Na2S.  Determine  antimony  and  arsenic  as 
described  under  slime  analysis. 

The  insoluble  sulphides  of  lead,  bismuth,  copper,  and  sil- 
ver may  be  dissolved  in  nitric  acid,  neutralized  with  sodium, 
carbonate,  and  KCN  added.  Lead  and  bismuth  carbonates 
are  filtered  off,  the  filtrate  acidified  with  H2S04  under  the 
hood,  AgCN  filtered  off  and  the  solution  boiled  to  expel  all 

*  "Quantitative   Chemical   Analysis    by   Electrolysis."     Classen-Herrick- 
Boltwood    265. 


300  LEAD  REFINING  BY  ELECTROLYSIS. 

HCN,  after  which  copper  is  determined  in  the  solution  as  fol- 
lows: Nearly  neutralize  the  solution  with  ammonia,  keeping 
the  bulk  small,  say  50  cc.,  add  ammonium  acetate,  and  divide 
into  two  equal  parts.  Add  to  one  part  a  fair  excess  of  potas- 
sium ferrocyanide  solution,  and  filter  off  the  red  precipitate 
immediately,  passing  through  the  paper  twice  if  necessary. 
Add  1  cc.  acetic  acid  to  each  and  the  same  amount  of  potas- 
sium ferrocyanide  to  the  unfiltered  half,  and  match  the  color 
in  the  filtered  half  by  adding  a  weak  copper  sulphate  solu- 
tion of  known  strength  from  a  burette,  allowing  one  minute 
between  each  addition  of  copper  sulphate,  for  the  color  to 
develop.* 

The  silver  cyanide  precipitate  is  not  desired,  for  silver  is 
determined  by  cupelling  a  separate  sample  of  the  lead. 

To  determine  bismuth,  dissolve  the  carbonates  of  lead 
and  bismuth  in  dilute  nitric  acid  and  precipitate  as  BiOCl, 
by  Ledoux's  method,  as  described  under  "Slime." 

To  be  sure  of  the  results  it  is  necessary  to  run  a  check 
analysis  on  the  nitric  and  sulphuric  acids,  evaporating  the 
same  amount  of  them  down  nearly  to  dryness,  and  treating 
the  last  of  the  sulphuric  acid  in  the  same  way  as  the  lead 
sample. 

The  results  of  refined  lead  analysis  are  more  apt  to  depend 
on  the  chemist  than  on  the  lead,  and  it  is  desirable  that  as 
many  errors  as  possible  be  eliminated  to  get  accurate  results. 
One  of  the  causes  of  error  is  in  the  chemicals  used,  which  are 
not  absolutely  pure  of  course,  and  import  certain  quantities 
of  iron,  copper,  arsenic,  and  antimony.  The  amount  of  nitric 
and  sulphuric  acid  used  is  as  great  as  the  lead  sample,  so  that 

*Crooke's  "Select  Methods  of  Chemical  Analysis,"  page  338. 


ANALYTICAL  METHODS   AND   EXPERIMENTAL  WORK.     301 


a  check  should  be  run  on  the  acids.  On  one  occasion  I  deter- 
mined copper  in  lead  as  .0010%,  but  on  running  a  check  on 
the  acid,  it  was  discovered  that  there  was  no  copper  in  the 
lead,  but  it  all  came  from  the  chemicals. 

The  following  show  the  variation  of  results  on  the  same 
sample  of  electrolytic  lead: 

TABLE   119. 


Fe 

Zn 

Sb 

Cu 

As 

Bi 

Ag 

Chemist  . 

.00023% 
.  00032% 
.00040% 

.0004% 

.0007% 

.00043% 
.00045% 
.00045% 

.00005% 

None 

.  00003% 

Betts 

.0022  % 
0037  % 

.0079% 
0042% 

.0013% 
0007% 

.0013  % 
0012  % 

.0065  % 
0092  % 

.00016% 
0003  % 

New  York 

No.  1 

New  York 

No.  2 

As  the  lead  was  deposited  electrolytically  and  could  have 
contained  no  zinc,  the  figures  by  2  and  3  are  certainly  wrong. 
My  iron  and  copper  determination  was  made  in  triplicate  and 
all  results  agreed  fairly  well,  especially  for  copper.  There  is 
no  agreement  at  all  for  arsenic  and  silver,  but  I  have  no  con- 
fidence in  my  own  figures  for  these  elements.  As  it  would  be 
easy  to  introduce  traces  of  iron  into  the  sample,  unless  hammered 
or  rolled  with  care,  I  think  my  own  figures  are  nearer  right. 
The  same  remark  applies  to  the  presence  of  iron  in  the  lead 
as  to  zinc.  As  the  precipitated  lead  sulphate  may  take  out 
some  antimony,  the  figures  for  Sb  .0007%  by  two  chemists 
are  apt  to  be  slightly  too  low. 

The  following  analyses  were  made  in  the  same  sample,  one 
at  Trail,  by  Dr.  Wm.  Valentine,  and  one  by  Messrs.  Ledoux  & 
Co.,  of  New  York. 


302  LEAD  REFINING   BY   ELECTROLYSIS. 

TABLE   120. 


Cu 

Sb 

Fe 

Sn 

Ag 

.0003% 
.0020% 

.0060% 
.0010% 

.0003% 
.0046% 

.0049% 
.0095% 

.0006% 
.0006% 

Valentine 
Ledoux  &  Co. 

The  agreement  in  the  case  of  silver  is  satisfactory. 
The  lower  figures  for  iron  and  copper  show  less  con- 
tamination of  the  sample  mechanically  or  by  chemicals, 
Dr.  Valentine's  Sn  +  Sb  =  0.105%  and  Ledoux  &  Co.'s  Sn  +  Sb 
=  .0109%,  so  that  the  separation  was  probably  not  complete 
in  one  case. 

Antimony,  arsenic,  and  tin  are  determined  by  us  in  the 
sulphide  solutions  by  electrolysis.  Antimony  only  is  removed 
when  the  solution  is  electrolyzed.  This  is  an  accurate 
method. 

Slag  from  fusing  slime. — This  contains  antimony,  arsenic, 
lead,  bismuth,  copper,  iron,  silica,  and  sulphur.  Dissolve  in 
HC1,  add  KClOs,  boil  out  chlorine,  neutralize  with  sodium 
carbonate,  and  determine  antimony  and  arsenic,  as  in  making 
slime  analyses.  The  insoluble  sulphides  may  also  be  further 
analyzed  as  in  the  slime  analysis. 

Electrolyte. — To  determine  acidity,  the  following  method 
was  in  use  at  Trail.  Add  an  equal  volume  of  alcohol  to  the 
sample  and  titrate  with  KOH  and  phenolphthalein,  correcting 
for  iron  and  alumina.  To  determine  lead  add  H2S04,  filter 
and  determine  lead  by  the  molybdate  method.  The  following 
method  is  used  in  my  laboratory:  Add  alcoholic  potassium 
acetate  solution.  Filter  off  K2SiF6,  wash  with  diluted  alcohol, 
add  paper  and  precipitate  to  distilled  water  in  a  beaker,  heat 
to  boiling  and  titrate  with  NaOH,  using  rosolic  acid  preferably, 


ANALYTICAL  METHODS   AND   EXPERIMENTAL  WORK.     303 

but  also  phenolphthalein  as  indicator.  Lead  is  determined 
as  described  above.  Also  the  analysis  may  be  made  by 
adding  neutral  ammonium  sulphate,  filtering  and  determining 
lead  sulphate.  Titrate  filtrate  with  cochineal  and  standard 
ammonia  in  the  cold.  Other  determinations  on  electrolyte 
are  seldom  made.  For  free  HF,  add  to  hot  solution,  hot  boric 
acid  of  known  strength  until  a  permanent  precipitate  of  silica 
results. 

Reaction : 

4HF  +  B  (OH)3  -  BHF4  +  3H20. 

Also  remove  lead  with  H2S  filter,  let  stand  till  H2S  has  passed 
off  or  oxidized,  and  determine  HF  and  H2SiF6  as  described 
under  the  analysis  of  fluosilicic  acid,  page  177. 

Copper-silver  matte  from  melting  slime. — To  determine 
sulphur,  dissolve  in  concentrated  nitric  acid.  All  or  nearly 
all  of  the  sulphur  oxidizes.  Dilute  and  filter.  Remove  silver 
from  filtrate  with  HC1,  add  filtrate  to  insoluble  portion,  add 
KClOa  and  evaporate  to  dryness.  Add  HC1,  to  dissolve  salts, 
then  add  ammonia  until  slightly  alkaline,  and  filter.  Add  HC1 
and  BaCl2  to  filtrate.  To  determine  lead,  copper,  and  silver 
dissolve  1  gr.  in  boiling  concentrated  sulphuric  acid,  cool, 
dilute,  filter  off  PbS04  and  titrate  by  Alexander's  molybdate 
method.  Determine  silver  in  filtrate  with  NH4CNS  solution, 
filter,  add  ammonia,  filter,  and  determine  copper  in  filtrate 
with  KCN.  To  determine  antimony  fuse  1  gr.  in  porcelain 
crucible  with  3  gr.  sulphur  and  4  gr.  sodium  carbonate, 
take  up  in  water,  filter,  add  H2S04  to  precipitate  sulphides, 
dissolve  sulphides  in  HC1  and  KC103,  boil  out  chlorine,  reduce 
with  sodium  sulphite,  boil  out  S02  and  titrate  with  perman- 
ganate. In  determining  antimony  in  the  chloride  solution  by 


304  LEAD  REFINING  BY  ELECTROLYSIS. 

permanganate,  the  solution  should  be  cool  and  of  consider- 
able volume,  and  must  contain  enough  HC1  to  prevent  the 
formation  of  a  brown  color  on  adding  permanganate  and  not 
enough  to  decompose  permanganate  fast  enough  to  interfere 
with  the  end  point.  In  reducing  with  sodium  sulphite,  I  add 
the  sodium  sulphite  to  the  solution  containing  say  \  to  J  strong 
HC1,  and  heat  to  boiling  very  slowly  to  give  the  SO 2  plenty 
of  time  to  act.  Then  boil  off  say  J  the  total  volume,  cool, 
dilute  somewhat,  perhaps  adding  HC1,  and  titrate.  To  make 
sure  of  the  result  more  sodium  sulphite  and  HC1  may  be  added 
after  finishing  the  titration,  solution  gradually  heated,  then 
boiled  and  titrated  again. 

Method  of  determining  silica  in  slime. — Five  gr.  of  slime 
is  treated  with  moderately  strong  HNOg  and  boric  acid,  fil- 
tered, silver  precipitated  by  HC1,  evaporated  to  dryness  several 
times  with  HC1.  The  residue  from  the  nitric  acid  was  dis- 
solved in  HC1  and  solution  evaporated  to  dryness  several  times 
with  HC1.  Both  of  these  evaporations  were  taken  up  with 
HC1  and  the  insoluble  material  filtered  off.  The  residue  of 
the  slime  from  the  treatment  with  HC1  was  treated  with  aqua 
regia  and  insoluble  material  filtered  off.  All  the  insoluble 
matter  was  ignited  together,  weighed,  pure  HF  added,  HF 
and  H2SiF6  driven  off,  and  residue  weighed  again,  calling  the 
difference  silica. 

Antimony  fluoride  solution. — It  is  frequently  convenient 
to  titrate  this  with  permanganate,  after  diluting  the  sample 
with  water  and  HC1.  If  a  strong  yellow  color  develops,  the 
result  is  too  high,  and  the  proportion  of  HC1  was  not  high 
enough,  or  the  sample  was  too  concentrated.  The  solution 
can  be  standardized  against  ferrous  iron;  56  parts  iron  =  60 
parts  antimony. 


ANALYTICAL  METHODS  AND   EXPERIMENTAL  WORK.     305 

Experimental  work. — Preparation  of  fluosilicic  acid.  Put 
hydrofluoric  acid  15-20%  strength  in  a  lead  pan  and  add  excess 
of  finely  powdered  calcined  flint ,  which  dissolves  more  readily 
than  quartz.  Heat,  but  not  to  boiling,  until  solution  is  satu- 
rated with  silica,  or  until  pungent  smell  of  HF  has  stopped 
coming  off.  To  make  the  lead  solution,  add  the  right  amount 
of  white  lead,  which  ordinarily  contains  80%  of  metallic  lead. 
Gelatine  or  glue  is  added  to  the  electrolyte  in  the  form  of  a 
strong,  hot  solution  in  water. 


FIG.  66. 

Small  electrolytic  tanks  can  be  conveniently  made  of  wood, 
and  soaked  or  dipped  in  hot  paraffine  for  some  time.  After 
cooling  a  layer  of  paraffine  can  be  put  on  the  wood  by  letting 
it  cool  inside,  then  adding  paraffine  and  turning  the  box  in 
various  positions.  This  makes  a  good  tank  for  refining 
experiments. 

To  provide  circulation,  arrangements  for  experiments  as 
shown  in  Fig.  66  are  convenient.  The  tanks  are  rectangular 
and  conditions  as  to  current  density,  voltage,  solution,  tempera- 
ture, products,  etc.,  may  be  as  exactly  determined  as  on  a  large 
scale. 


306  LEAD  REFINING  BY  ELECTROLYSIS. 

Conductivity  measurements  are  made  with  sufficient  accu- 
racy for  practical  purposes,  by  using  a  small  paraffined  box 
about  3  inches  square  and  deep,  with  two  pure  lead  sheets 
at  each  end.  If  the  width  of  the  box  is  known  and  the 
volume  of  the  solution  is  measured,  the  cross-sectional  area 
can  be  calculated.  Current  is  passed  through  while  the 
solution  is  stirred,  and  the  resistance  calculated  from  the 
ammeter  and  voltmeter  readings.  As  the  polarizing  e.m.f. 
in  depositing  lead  is  under  .02  volt,  the  method  is  suffici- 
ently accurate. 

In  antimony  depositing  with  lead  rods  as  anode,  practical 
work  may  be  duplicated  with  one  anode  by  using  a  tall  par- 
affined box  with  a  full-length  anode.  The  box  is  about  3  inches 
square  inside,  and  faithfully  represents  a  full-size  tank,  which 
comprises  only  a  large  number  of  the  same  units,  without  the 
intervening  walls. 

In  experimenting  on  small  quantities  of  slime  it  can  be 
cooked  up  with  solutions  in  porcelain  evaporating  dishes.  For 
10  or  20  Ibs.  large  stoneware  crocks  holding  60-80  litres  are 
good.  Steam  can  be  turned  in  through  a  lead  pipe  for  heating 
and  stirring.  Antimony  fluoride  solutions  can  be  handled  in 
painted  lead  tanks  or  paraffined  wooden  ones.  To  roast  slime 
with  sulphuric  acid  it  is  sufficient  to  spread  it  on  a  cast-iron 
plate  heated  underneath. 

For  ferric  sulphate  electrolysis  on  a  small  scale  a  tank,  as 
shown  in  Fig.  67,  taking  25-50  amperes  is  useful.  The 
anodes  are  cast  in  lead  in  a  slit  cut  in  a  board,  and  hung  with 
two  narrow  boards  from  the  ceiling.  For  work  lasting  only 
a  few  weeks  the  lead  tank  and  diaphragm  can  be  soldered 
together  with  coarse  solder,  2  or  3  parts  of  lead  to  1  of 
tin. 


ANALYTICAL  METHODS  AND   EXPERIMENTAL  WORK.     307 

For  reduction  of  lead-antimony  slags,  use  a  lead  pan  in  which 
the  slag  is  spread  out  and  made  cathode  with  a  sheet-lead  plate 
for  anode  just  above  the  cathode.  For  reduction  in  the  fused 


FIG.  67. 


state  lead  chloride  (from  precipitating  lead  nitrate  or  acetate 
with  NaCl)  is  melted  in  a  porcelain  crucible,  and  two  carbon 
electrodes  dipped  in.  The  reduced  metal  drops  from  the  nega- 
tive electrode  to  the  bottom  of  the  crucible.  It  is  necessary  to 


308  LEAD  REFINING  BY   ELECTROLYSIS. 

have  the  crucible  well  covered  to  keep  the  air  out.     The  slag 
is  fed  from  time  to  time  as  reduced. 

An  experimental  tank  for  one  full-sized  lead  anode,  about 
6  inches  wide,  30  inches  long,  and  42  inches  deep,  with  one 
glass  end,  was  built  at  Trail,  to  watch  the  behavior  of  the 
anode  slime.  This  was  not  successful  in  that  particular 
instance  because  the  solution  happened  to  be  too  dark  and 
turbid. 


CHAPTER  XI. 

BIBLIOGRAPHY. 

KEITH  PROCESS.    Engineering  and  Mining  Journal,  1878,  Vol.  XXVI, 

page  26. 
TOMMASI  PROCESS.    Comptes  Rendus,  1896,  Vol.  122,  page  1476;  also 

Zeitschrift  fur  Elektrochemie,  Vol.  Ill,  1896-97;  92,  310,  341. 
GLASER,  Deposition  of  Lead.    Zeitschrijt  fur  Elektrochemie,  Vol.  VII, 

1900,  pages  365-369  and  381-386. 
BORCHERS.    Lead  Refining  with  Fused  Baths.    "Electric  Smelting 

and  Refining."     First  English  Edition. 
SENN.    Zur   Kenntniss   der   Elektrolytischen   Bleiraffination.      Zeit- 

schrift  fur  Elektrochemie,  1905,  Vol.  XI,  page  229. 
MENNICKE.    Elektrische  Zinngewinnung  und  Zinnraffinationmit  Fluss 

und  Kieselflussaure.    Zeitschrift  }ur  Elektrochemie,  Vol.  XII,  1905, 

pages,  112,  136,  161,  181. 
WHITEHEAD.    Electrolytic  Refining  of  Lead,  etc.    Mines  and  Minerals, 

Vol.  XXV,  1905,  page  288. 
JACOBS.    Lead  and  Silver  Refining  at  the  Canadian  Smelting  Works, 

Trail,  B.  C.    British  Columbia  Mining  Record,  December,  1904, 

page  410. 
BETTS.    Electrolytic  Lead  Refining.    "Trans.  Am.  Institute  of  Mining 

Engineers,"    also    Electrochemical    and    Metallurgical    Industry, 

August,  1903,  page  407. 
HABER.    Electrochemical  Industry.    Vol.  I,  1903,  page  381.    Report 

on  Electrochemistry  in  the  United  States.    Zeitschrift  fur  Elek- 
trochemie, 1903,  page  390. 

309 


310  LEAD   REFINING  BY  ELECTROLYSIS. 

ULKE.  The  Electrolytic  Refining  of  Base  Lead  Bullion.  Engineering 
and  Mining  Journal,  1902,  October  llth. 

BEITS.  Electrolytic  Treatment  of  Electrolytic  Slime.  Electrochemical 
and  Metallurgical  Industry.  1905,  Vol.  Ill,  pages  141,  235. 

-Pamphlets  for  Free  Distribution.    September,  1901;  March,  1904. 

HOFMAN.  Recent  Improvements  in  Lead  Smelting.  Mineral  Indus- 
try, Vol.  XI,  1902,  page  453;  Vol.  XIV,  1905,  page  421. 

BETTS  AND  KERN.    The  Lead  Voltameter.    Vol.  VI,  1904,  page  67. 

BETTS,  A.  G.  Electrolytic  Process  of  Refining  Lead.  (Use  of  Fluo- 
silicic  Acid,  etc.)  United  States,  679824,  August  6th;  Mexico 
2144,  August  19,  1901;  Canada  72068,  July  2,  1901,  assigned 
to  Canadian  Smelting  Works;  Great  Britain,  1758  of  January 
25,  1901;  Spain  28516,  September  16,  1901,  lapsed;  Australia 
1205,  August  3,  1904. 

-  Electrodeposited  Lead.  United  States  713278,  November  11,  1902, 
reissue  12117,  June  9,  1903. 

—  Electrolytic   Refining   of  Lead  and  Lead   Alloys.    (Deposition  of 

Solid  Lead.)  United  States  713277,  November  11,  1902,  reissue 
12301,  January  3,  1905;  Australia  1226,  August  5,  1904;  Spain 
29567,  July  2,  1902,  lapsed;  Italy  156177,  July  23,  1902,  lapsed; 
Mexico  2261,  July  3,  1902;  Canada  77357,  September  9,  1902, 
assigned  to  Canadian  Smelting  Works;  Great  Britain  7661  of  1902, 
April  1st;  Germany  31374  B,  40  C,  April  1,  1902,  pending; 
France  320097,  August  9,  1902,  lapsed;  Belgium  162413,  April  1, 
1902,  lapsed. 

—  Apparatus  for   Refining  Lead  by  Electrolysis.    (Compression  of 

Deposited  Lead.)     United  States  679357,  July  30,  1901;    South 
Australia  5354,   August  8,   1901;    Great  Britain, 
lapsed;   Germany  134861,  July  30,  1902,  lapsed. 

—  Process  of  Treating  Anode  Residues.    (With  Chlorine.)     United 

States  712640,  November  4,  1902. 

-Plant  for  the  Electrodeposition  of  Metals.  United  States  789353, 
May  9,  1905. 


BIBLIOGRAPHY.  311 

—  Process  of  Treating  the  Metal  Mixture  Produced  as  a  By-product 

in  Electrolytic  Metal  Refining  Operations.  United  States  793039, 
June  20,  1905;  Mexico  filed  May  8th,  granted  July  8,  1905; 
Great  Britain  15298  of  1904;  Australia  3050,  April  27,  1905; 
Canada  94675,  March  27,  1905;  Germany  B39592,  pending. 

—  Process   of  Electrodepositing   Antimony.     United  States  792307, 

June  13,  1905;  Mexico  May  8,  1905;  Canada  94674,  August  15, 
1905;  Australia  3049,  April  27,  1905;  Great  Britain  15294,  of 

1904,  July  8th. 

—  Electrolytic  Apparatus.  (Making  Ferric   Sulphates,   etc.)     United 

States  850127,  April  16,  1907. 

—  Apparatus    for    Refining    Lead    by    Electrolysis.      (Copper-lined 

Tank.)    United  States  803543,  November  7,  1905. 

—  Electrolytic  Process,  Using  Insoluble  Anodes.    (Making  Ferric  Sul- 

phate, etc.)    United  States  803543,  November  7,  1905. 

—  Electrolytically  Refining  Silver.     (Methyl-sulphate    Parting,  etc.) 

United  States  795887,  August  1,  1905.  Canada  94676,  March  27, 
1905. 

—  Electrolytically    Refining    Metals.      Canada    94676,    March    27, 

1905.  United  States  June  18,  1907. 

—  Apparatus  for  Refining  Lead  by   Electrolysis.    (Systems  of  Con- 

tacts.)   U.  S.  No.  827702. 

KERN,  E.  F.,  assignor  to  A.  G.  BETTS.  Treating  Anode  Slime.  (Roast- 
ing with  Sulphuric  Acid.)  U.  S.  No.  863601,  November  7,  1905. 

TRUSWELL,  R.    Anode  Mold.    United  States  823977,  June  19, 1906. 

MILLER,  J.  F.  Method  of  Lining  Tanks  for  Electrolytic  Work. 
U.  S.  Patent  857886,  June  25,  1907. 

-—Casting  Metal  Sheets.  One-half  assigned  to  W.  H.  Aldridge. 
U.  S.  Patent  857885,  June  25,  1907. 


APPENDICES. 

APPENDIX  I. 

PLANT  OF  THE  CONSOLIDATED  MINING  AND  SMELTING  COMPANY 
OF    CANADA,    LIMITED,    AT    TRAIL,    BRITISH    COLUMBIA. 

THE  pioneer  electrolytic  lead  refinery  is  that  of  the  above 
company,  which  is  located  on  the  west  bank  of  the  Columbia 
River  a  few  miles  north  of  the  international  boundary.  Trail 
has  railroad  connection  with  Rossland,  which  in  turn  is  reached 
by  the  Great  Northern  Railroad,  and  is  also  connected  with 
the  Canadian  Pacific  system  at  the  north. 

The  Trail  plant  has  been  operated  since  1902,  with  some 
interruptions  for  enlargements,  and  has  a  present  capacity  of 
80  tons  per  day,  although  the  bullion  received  to  be  treated 
at  present  amounts  to  only  about  45  tons  per  day.  It  will 
probably  be  only  a  short  time  before  sufficient  lead  will  be 
locally  produced  to  keep  the  plant  running  at  its  full  capacity. 
The  operations  and  plant  have  been  brought  to  a  high  standard 
by  the  capable  management,  and  many  good  points  have  been 
developed  that  should  be  noted. 

Power  is  supplied  by  the  West  Kootenay  Light  and  Power 
Company  from  their  plant  at  the  Bonnington  Falls,  about  25 
or  30  miles  north,  in  the  form  of  three-phase  sixty-cycle  cur- 
rent, I  believe  at  22,000  volts.  It  is  transformed  to  550  volts 
at  a  sub-station  about  a  quarter  of  a  mile  from  the  refinery, 

312 


APPENDIX.  313 

and  near  the  smelter.  At  the  refinery  power  plant  there  is 
a  Canadian  General  Electric  600  H.P.,  60-cycle,  550-volt  motor 
directly  connected  to  a  3600-ampere,  60-110  volt  electrolytic 
generator  of  the  same  make,  which  supplies  power  to  the  lead- 
depositing  tanks.  A  Westinghouse  165  H.P.,  550  volt,  three- 
phase  motor  is  directly  connected  to  a  105  K.W.,  30- volt,  3500- 
ampere,  580-rpm.  electrolytic  generator  of  the  same  make,  which 
at  present  supplies  current  to  the  electrolytic  antimony-deposit- 
ing tanks.  For  power  purposes  there  is  a  20  K.W.,  125-volt 
direct-current  generator  that  supplies  power  to  the  crane.  The 
crane  uses  about  2  H.P.  when  running.  The  pumps  require 
2-3  H.P.,  using  a  three-phase  motor,  and  the  centrifugal  lead- 
pumps  use  about  3  H.P.  each  against  a  six-foot  head  of  lead. 
Probably  the  average  power  in  use  for  power  purposes  does 
not  reach  5  H.P.  and  the  maximum  in  use  is  about  12  H.P. 

The  tank-room  50  feet  wide  and  315  feet  long  is  subdivided 
about  as  follows:  Adjoining  the  south  end  there  is  a  room  about 
18  by  40  feet  in  which  the  cathodes  are  hung  and  straightened. 
In  the  main  building  is  first  a  clear  space  of  about  4  feet  from 
the  wall;  next  comes  a  block  of  132  tanks  occupying  a  length 
of  about  96  to  97  feet.  These  tanks  are  in  six  double  cas- 
cades, 11  tanks  long,  the  highest  tanks  being  47  inches  and 
the  lowest  20  inches  above  the  floor,  which  is  level. 

At  the  low  end  of  these  tanks  is  a  small  space  for  solution 
launders,  and  then  comes  a  row  across  the  building  of  clean- 
ing-tanks, 7  feet  6  inches  long  and  6  feet  3  inches  wide.  Then 
comes  a  17-foot  clear  space  with  a  floor  of  cast-iron  plates. 
This  space  is  used  for  electrode  storage,  the  electrodes  resting 
on  small  cars,  and  also  for  working  space.  Then  there  is 
another  row  of  six  washing-tanks  of  the  same  size,  followed  by 
a  three-foot  space  for  launders  and  bus-bar  connections,  and  a 


314  LEAD   REFINING  BY  ELECTROLYSIS. 

block  of  72  tanks  in  six-tank  cascades  which  occupies  54  feet 
of  the  length  of  the  building.  Then  there  is  a  three-foot  space 
for  launders  and  bus-bar  connections,  followed  by  60  tanks 
in  five-tank  cascades  =  44  feet.  These  latter  tanks  have  not 
yet  been  used  on  account  of  the  present  scarcity  of  bullion 
to  be  treated,  though  they  are  going  to  be  put  in  commission 
soon,  while  the  current  flowing  will  be  reduced  as  long  as  the 
shortage  of  bullion  lasts.  Instead  of  using  less  than  the  full 
number  of  tanks,  all  the  tanks  will  be  worked  with  a  smaller 
current.  Then  there  is  a  set  of  electrode  storage  racks  about 
16  feet  long,  which  occupy  the  full  width  of  the  building, 
excepting  the  aisles. 

The  remainder  of  the  building  is  occupied  by  the  melting 
floor  and  contains  the  lead  and  bullion  kettles  and  casting 
floor.  In  a  small  side  room  is  the  apparatus  for  making  start- 
ing sheets.  There  is  also  in  one  corner  a  lead-pipe  machine. 
The  floor  is  subdivided  into  first  a  25-foot  clear  space  to  the 
lead  kettles,  then  the  lead  kettles  take  12  feet.  Then  there 
is  another  twenty-five  foot  clear  space  to  the  bullion  kettles, 
which  are  placed  toward  one  side  of  the  centre  of  the  build- 
ing and  occupy  12  feet  of  its  length,  with  a  final  space  at  the 
end  of  about  18  feet. 

The  tanks  are  of  four-inch  fir  with  bolts  passing  through 
the  wood  and  are  similar  to  Fig.  38.  Mr.  John  F.  Miller  has 
described  to  me  his  method  of  lining  tanks.*  He  uses  two 
grades  of  California  asphalt,  "hard  "  and  "D"  grade.  These 
are  mixed  in  the  proportions  required  to  give  a  melting  point 
of  45°  C.  Mr.  Miller  determines  the  melting  points  of  the 


*  Mr.  Miller    has  applied  for  United    States   patents  on  his  tank  and 
method  of  lining  it. 


APPENDIX. 


315 


mixtures  by  molding  them  into  cones  about  4  inches  high,  and 
keeps  them  in  a  water-bath  of  a  certain  temperature  for 
twenty-four  hours.  If  the  cone  does  not  show  any  altera- 
tion in  shape  in  that  time,  the  melting-point  is  some  higher 
temperature,  and  if  it  runs  at  all,  the  melting-point  is  some 
lower  temperature. 

The  seams  of  the  tank  are  made  as  shown  in  the  sketch 
(Fig.  68).  The  tank  is  placed  in  various  positions,  the  side 
being  treated  being  of  course  horizontal.  The  seam  is  first 


FIG.  68. 


FIG.  69. 


FIG.  70. 


filled  with  several  layers  of  asphalt  by  running  along  the  seam 
with  a  teakettle  holding  the  hot  mixture.  After  the  seams 
are  all  filled  on  that  side,  it  is  then  flooded  with  an  asphalt 
layer  about  one-quarter  inch  thick.  Two  men  can  line  two 
double  tanks  per  day.  The  tanks  in  the  refinery  are  giving 
excellent  satisfaction.  Though  in  use  two  years  they  have 
not  yet  required  any  repairs.  There  is  little  or  no  absorption 
of  the  solution  by  the  wood,  as  is  the  case  with  merely  painted 
wood  tanks. 

There  are  two  styles  of  bus-bars  in  the  refinery,  as  shown 
in  Fig.  69.  They  and  the  cathode  cross-bars  are  kept  scrupu- 
lously polished  so  the  contact  losses  are  only  from  .01  to  .05 


316  LEAD  REFINING   BY   ELECTROLYSIS. 

volt  for  each  contact,  averaging  about  .02  volts  or  less.  There 
are  three  sets  of  contacts  to  the  tank,  bus-bar  to  anode, 
cathode  to  cathode  cross-bar,  and  cathode  cross-bar  to  bus- 
bar. Small  iron  clips  are  driven  on  the  cathode  and  cathode 
bar,  after  the  tank  has  been  loaded,  to  ensure  good  contact 
throughout  the  tank.  The  clips  are  as  shown  in  Fig.  70. 

The  anodes  are  cast  in  closed  upright  molds,  ten  at  a  time, 
similar  to  Fig.  71,  which  shows  some  new  molds  that  have 
been  ordered  differing  from  those  at  present  in  use  only  in 
that  they  are  to  be  made  of  steel  instead  of  cast  iron,  the  taper 
allowed  for  withdrawing  the  lead  is  to  be  less,  and  the  size 
of  the  anode  head  is  reduced.  Mr.  Miller  has  applied  for  a 
United  States  patent  on  this  mold. 

The  main  body  of  the  mold  only  is  to  be  made  of  steel, 
and  the  wedge  is  to  be  of  cast  iron.  The  present  molds  ope- 
rate very  well,  and  when  the  anodes  are  lifted  by  power  three 
or  five  at  a  time,  instead  of  by  a  chain-block  as  at  present,  the 
cost  for  labor  per  ton  cast  is  not  expected  to  exceed  20  cents, 
though  at  present  it  is  higher,  namely  about  27  or  28  cents 
per  ton,  with  wages  of  35  cents  per  hour.  The  molds  are 
placed  upright  in  a  wood  box  arranged  with  a  set  of  water 
sprays  to  cool  each  mold.  The  lead  is  pumped  from  the  kettle 
into  the  mold  with  a  centrifugal  pump,  which  was  originally 
a  water-pump.  This  pump  remains  at  the  bottom  of  the 
kettle  continuously  and  has  already  been  in  use  for  a  long 
time  with  no  repairs  or  cleaning.  It  is  driven  by  a  3-H.P. 
motor  through  a  belt  and  gearing.  See  Plate  10. 

The  anodes  weigh  370  to  380  pounds  each.     At  present 
the  percentage  of  scrap  returned  to  be  remelted  is  about  20 
but  this  will  be  considerably  reduced  with  the  new  molds, 
which  will  make  smaller  lugs. 


APPENDIX. 


317 


-#B?*-W 

3£ 


318 


LEAD  REFINING   BY   ELECTROLYSIS. 


The  anodes  are  lifted  by  man  power  with  a  chain-block 
and  stacked  in  a  vertical  position,  with  the  same  spacing  as 
is  used  in  the  depositing-tanks,  in  cars  holding  ten  anodes 
each.  There  are  40  of  these  cars  at  the  plant.  Before  lifting 


FIG.  72. 

into  the  tanks  two  cars  are  run  together,  and  a  spacing-board 
protected  from  wear  by  sheet  iron  is  placed  over  the  top  to 
give  the  exact  spacing.  (Figs.  72  and  73.) 

The  anodes  remain  in  the  tanks  eight  or  nine  days  when 
the  full  current  is  passing,  giving  two  crops  of  cathodes  four 


FIG.  73. 


to  five  days  old.  The  production  of  only  one  crop  of  cathodes 
per  set  of  anodes  has  been  tried  and  it  is  contemplated  to 
go  back  to  it,  from  which  one  would  conclude  that  the  cost 
of  refining  was  about  the  same  either  way. 


APPENDIX. 


319 


The  anode  scrap  with  most  of  the  slime  still  adherent  is 
lifted  by  the  crane,  a  portable  tray  (Fig.  74)  is  hung  under- 
neath the  load  by  the  "  crane  chasers/'  when  the  crane  car- 
ries the  whole  to  one  of  the  large  washing  tanks,  where  it  is 
deposited,  while  the  scrap  is  handled  therefrom  individually 
on  a  chain-block  by  the  men  who  clean  scrap.  This  requires 
three  men  on  one  shift.  The  cleaned  scrap  is  thrown  on  a 
small  flat  car  and  wheeled  to  the  bullion-kettle  and  dumped 
in. 

The   cathodes  are  made  on  the  sloping  table,   one  man 


FIG.  74. 

making  400  sheets  in  eight  hours,  while  the  night  watchman 
makes  200  to  250  sheets  during  the  night  while  not  engaged 
in  his  other  duties.  The  sheets  are  taken  on  small  flat  cars 
to  the  hanging  room,  where  they  are  placed  on  a  table,  flattened 
out,  wrapped  around  the  cathode  cross-bars  two  or  three 
times,  the  men  using  a  stick  to  bring  the  lead  close  to  the 
copper.  They  are  then  hung,  21  to  the  load,  on  small  cars 
provided  with  convenient  supports.  To  place  them  in  the 
tanks  they  are  wheeled  through  the  aisle  to  a  position  oppo- 
site the  tank,  and  a  man  stands  over  the  tank,  reaches  over 


320  LEAD  REFINING   BY  ELECTROLYSIS. 

to  the  car  and  lifts  the  sheets  one  at  a  time  into  the  tank. 
The  entire  operation  of  charging  a  tank  with  cathodes,  fixing 
the  spacing  and  contacts,  and  wheeling  the  car  to  the  tank 
and  away  again  requires  about  fifteen  minutes  for  one  man. 
For  lifting  cathodes  to  and  from  the  tank,  two  styles  of  lift- 
ing racks  are  used.  There  are  several  of  each  at  the  refinery. 
The  cathode  lifting  rack,  which  is  the  most  complicated,  may 
be  seen  in  Plate  11. 

The  finished  cathodes  are  lifted  by  the  crane,  the  same 
pan  being  placed  underneath  as  before,  when  the  load  goes 
to  a  washing  tank  where  it  is  deposited  and  any  slime  wiped 
off  and  the  plates  splashed  to  get  off  the  strong  solution. 
They  are  then  placed  by  the  crane  on  a  portable  rack  near  the 
melting  pot,  and  are  pushed  over  into  the  pot  by  hand,  which 
only  takes  a  minute  or  two,  the  cathode  cross-bars  of  course 
being  previously  pulled  out. 

The  cathodes  are  slowly  melted  down  during  the  day,  and 
on  the  evening  shift  the  pots  are  skimmed,  and  the  centrifugal 
pumps  lowered  into  the  lead  and  the  lead  molded.  The  lead 
launder  is  about  22  feet  long  and  there  are  some  160  molds 
in  the  circle.  A  crew  of  four  men  can  mold  about  20  tons 
per  hour,  but  they  do  not  work  as  fast  as  this,  as  the  two 
men  who  wheel  the  lead  to  the  box-cars  and  pile  it  in  them 
could  not  keep  up,  so  that  about  15  tons  per  hour  is  the  usual 
speed.  The  six  men  do  all  the  work,  including  firing,  skim- 
ming, and  loading. 

The  use  of  a  centrifugal  pump  for  raising  lead  gives  the 
best  satisfaction,  and  is  to  be  preferred  to  any  of  the  other 
methods.  This  idea  originated  with  Mr.  Miller,  of  the  Trail 
Company.  A  two-inch  pump  is  about  the  right  size,  and  costs 
about  $13.00  at  Seneca  Falls,  N.  Y.  It  is  necessary  to  find 


APPENDIX.  321 

the  right  speed  at  which  to  run  the  pump  before  it  can  be 
worked  satisfactorily. 

The  slime  is  collected  from  the  electrolytic  tanks,  after 
siphoning  off  the  clear  solution,  by  a  man  who  gets  into  the 
tank  with  a  pail  and  shovel,  and  raises  the  slime  by  hand 
into  a  copper  tank  about  15  by  30  inches  which  runs  on  a 
small  car  between  the  tanks.  A  piece  of  oilcloth  is  hung 
over  the  top  of  the  tank  and  of  the  copper  tank  to  keep  from 
losing  slime  and  getting  the  bus-bars  dirty.  No  pains  are 
taken  to  get  the  tank  entirely  clean,  but  on  the  contrary  con- 
siderable slime  is  usually  left  in  the  tank.  Quite  a  little  slime 
is  also  collected  from  the  large  washing  tanks,  a  hand-pump 
being  used  to  raise  the  slime  into  the  copper-tank  cars.  There 
are  six  of  these  cars  at  the  plant,  and  two  men  are  employed 
cleaning  tanks  and  taking  the  slime  to  the  slime  washing 
tanks.  The  slime  cars  are  hoisted  on  an  elevator  and  run 
on  rails  over  the  slime  washing  tanks.  A  plug  at  the  bot- 
tom of  the  tank  cars  is  raised  with  a  copper  wire,  when  the 
slime  drops  through  a  screen  into  the  washing  tanks.  Fre- 
quently a  hose  is  turned  into  the  tank  car  to  wash  out  the 
heavy  slime.  There  are  four  of  these  washing  tanks,  which 
are  of  wood,  side  by  side,  each  about  42  inches  wide,  8  feet 
long,  and  5  feet  deep.  The  decantation  method  of  washing 
is  in  use,  and  the  results  are  reported  on  a  slip  like  that  shown 
below.  The  slime  is  stirred  once  by  a  paddle,  and  steam  blown 
in.  After  settling,  the  clear  solution  is  siphoned  off  into  one 
of  three  launders  according  to  destination,  the  strong  solu- 
tion being  returned  to  the  electrolytic  tanks,  that  of  medium 
strength  going  to  the  evaporators,  while  the  weakest  is  used 
for  washwater.  The  solution  with  which  the  slime  is  satu- 
rated is  finally  reduced  to  about  2°  Beaume.  The  slime  is 


322 


LEAD   REFINING   BY   ELECTROLYSIS. 


finally  run  out  through  a  large  hose  fastened  into  one  end 
of  the  tank,  and  ordinarily  held  up  against  the  end,  into  sev- 
eral wood  suction-filters. 

TRAIL  REFINERY. 

SLIMES  WASHING. 
Date,  July  11,  1907. 


TANK  No.  4 

1 

FANK  No.  5 

Wash    No. 

Beaume. 

Destination. 

Wash  No. 

Beaume. 

Destination. 

Slimes 
Water.  .  . 
1  

30 
20 

Pump 

Slimes 
Water.  .  . 
1  

40 
30 

Pump 

2 

10 

Evaporator 

2 

20 

1  1 

3  
4 

6 
2 

i  f 
Washing 

3  
4 

10 

6 

Evaporator 

it 

5  
6 

0 

5  
6 

2 
0 

Washing 

TANK  No. 

L 

TANK  No. 

Wash    No. 

Beaume. 

Destination. 

Wash  No. 

Beaume. 

Destination. 

Slimes 
Water.  .  . 
1 

40 
22 

Pump 

Slimes 
Water.  .  . 
1  

30 
20 

Pump 

2  
3  

20 
10 

t  ( 
Evaporator 

2  
3  

10 
5 

Evaporator 
Washing 

4  

5 

4  

2 

5 

5 

0 

<  ( 

6 

6 

REMARKS: 


Signature. , 


APPENDIX.  323 

The  evaporation  of  the  washwater  is  conducted  in  a  wood 
tank  about  8  feet  square,  in  which  is  dropped  a  lead  pipe 
through  which  steam  is  passed.  The  acid  lost  during  the 
evaporation  is  three  pounds  SiF6  p'er  ton  lead  refined. 

Slime  treatment. — Mr.  Alexander  McNab's  method  of  treat- 
ing slime  is  now  used.  The  slime  from  the  washing  tanks 
is  first  sucked  dry  as  possible  on  the  suction-filters.  The 
slime  is  then  neutralized  by  stirring  into  it  a  little  caustic 
soda,  and  transferred  in  about  600-lb.  lots  to  one  of  six 
or  eight  large  iron  tanks  about  3  feet  wide,  8  feet  long,  and 
4  to  5  feet  deep.  The  tank  is  then  nearly  filled  with  the  so- 
dium sulphide  solution  as  it  runs  from  the  antimony  deposit- 
ing tanks,  and  25  Ibs.  of  sulphur  is  added.  It  is  stirred 
with  a  wood  paddle  once,  and  steam  turned  in,  which  is 
thereafter  sufficient  for  the  stirring.  After  about  two  hours' 
boiling  the  solution  is  settled  and  siphoned  off,  and  the  tank 
is  again  filled  with  sodium  sulphide,  sulphur  being  omitted 
this  time.  After  boiling  and  settling  again  the  clear  solu- 
tion is  siphoned  off  and  added  to  the  same  storage  tank  as 
the  first  lot.  The  slime  is  drained  and  treated  further  as  will 
be  described  below. 

The  sodium  sulphide  extracts  about  80%  of  the  anti- 
mony and  some  arsenic,  and  converts  a  good  part  of  the  re- 
maining metals  into  sulphides.  Contrary  to  what  would  be 
expected,  most  of  the  arsenic  remains  in  the  slime  until  the 
final  melting  to  dore  bullion.  The  sulphide  solution  con- 
tains about  3.5%  of  antimony  after  the  slime  treatment,  and 
varying  quantities  of  sulphide,  polysulphide,  and  thiosulphate. 
The  solution  is  collected  in  suitable  storage  tanks,  and  run 
through  a  series  of  antimony  depositing  tanks  of  iron,  with 
sheet  steel  cathodes  and  lead  anodes.  The  anodes  are  the 


324  LEAD  REFINING  BY  ELECTROLYSIS. 

same  kind  of  sheets  as  are  used  in  the  lead  depositing  tanks 
for  cathodes.  There  are  ten  of  these  tanks  in  two  cascades 
of  five  each.  They  have  each  about  240  square  feet  of  anode 
and  240  square  feet  of  cathode  surface,  and  can  take  a  cur- 
rent of  3000  to  3500  amperes  with  a  potential  when  working 
without  polarization  of  about  1.5  volts  each.  A  tempera- 
ture of  about  60°  C.  is  used  as  giving  the  highest  efficiency. 
The  iron  tank  is  itself  connected  as  cathode.  The  lead  anodes 
remain  in  working  condition  about  ten  days  and  are  then 
renewed.  The  current  efficiency  is  about  45%.  No  dia- 
phragms are  used.  The  solution  running  out  of  the  last 
tanks  contains  about  1%  antimony,  and  is  returned  to  be 
used  for  extracting  antimony  from  fresh  slime.  The  opera- 
tion of  the  tanks  is  entrusted  to  three  men,  one  on  each  shift. 
When  the  antimony  deposit  of  the  cathodes  gets  about  one- 
eighth  inch  thick,  they  are  taken  out  one  by  one  and  the  anti- 
mony knocked  off  by  hammering.  Each  tank  has  about 
20  cathodes  about  2  feet  wide  and  3  feet  deep.  The  sodium 
sulphide  is  changed  by  electrolysis  to  thiosulphate,  which 
means  a  heavy  loss  of  sodium  sulphide.  Attempts  will  be 
made  to  crystallize  out  the  thiosulphate  of  sodium  and  re- 
convert it  to  sulphide  by  reduction  with  carbon  at  a  red  heat. 
This  part  of  the  plant  is  running  at  a  loss  at  the  present  time, 
partly  on  account  of  a  drop  in  the  price  of  antimony,  but 
mainly  because  the  percentage  of  antimony  in  the  bullion  has 
recently  dropped  to  less  than  one-tenth  of  one  per  cent,  and 
the  percentage  extracted  by  the  sulphide  solution  is  much 
less  when  there  is  only  a  little  antimony  present.  The  anti- 
mony deposited  contains  a  little  arsenic,  which  can  be  re- 
moved if  too  much  is  present  by  melting  under  an  alkaline 
slag. 


APPENDIX.  325 

One  of  the  principal  items  of  cost  of  the  process  is  the 
heavy  cost  for  sodium  sulphide,  which  is  quite  expensive  when 
delivered  at  Trail.  Mr.  McNab  mentioned  that  the  loss  of 
Na2§  would  be  about  30  Ibs.  or  less  per  ton  of  Trail  bul- 
lion, without  recovery  or  regeneration  of  the  solution. 

To  use  this  process  continuously  it  would  be  very  necessary 
to  have  extremely  good  ventilation  where  the  sulphide  solu- 
tion is  stored  and  handled,  for  the  gases  given  off  are  inju- 
rious. 

The  treated  slime  has  run  as  high  as  27%  arsenic  and  4 
to  10%  antimony,  while  the  raw  slime  contains  perhaps  10% 
arsenic. 

The  deposited  antimony  contains-  some  gold  and  silver. 

The  slime  is  next  dried  in  a  large  iron  pan  placed  over 
the  roasting-furnace  flue,  with  a  hole  in  the  bottom,  so  that 
it  can  be  dropped  directly  into  the  furnace.  The  roasting- 
furnace  is  of  the  muffle  type,  and  is  hand  .raked.  Its  length 
for  the  hearth  appears  to  be  about  20  feet  and  width  about 
7  feet.  The  slime  is  calcined  at  a  very  low  heat  for  the  pro- 
duction of  the  oxides,  arsenates,  antimonates,  and  sulphides 
of  lead,  silver,  and  copper,  and  is  finally  raked  into  a  large 
steel  bucket  suspended  by  a  chain  block  from  an  overhead 
runway.  The  roasted  slime  is  leached  with  sulphuric  acid 
and  water,  taking  out  most  of  the  copper  and  one-third  to 
one-tenth  of  the  silver,  which  is  precipitated  by  metallic 
copper.  The  copper  sulphate  is  crystallized  out  and 
sold. 

The  residue  is  melted  in  a  magnesia-line  reverberatory 
furnace,  using  Crow's  Nest  Pass  coal,  with  silica  as  a  flux  to 
slag  off  the  lead.  This  is  a  tedious  operation,  as  the  lead  sul- 
phate and  silica  do  not  react  readily.  They  are  going  to  try 


326  LEAD  REFINING   BY  ELECTROLYSIS. 

my  suggestion  to  put  some  old  slag  in  each  charge  to  help 
the  melting.  The  parting  is  done  by  the  sulphuric  acid 
method,  and  the  copper  sulphate  is  crystallized  for  the  mar- 
ket. They  will  probably  try  another  suggestion  to  heat  the 
roasted  slime  with  sulphuric  acid  direct  to  make  nearly  all 
the  silver  soluble,  which  should  save  melting  the  silver 
twice. 

There  is  a  fluosilicic-acid  plant  which  distils  a  mixture  of 
fluorspar,  silica,  and  sulphuric  acid  in  iron  pans  about  8  feet 
diameter.  The  acid  fumes  are  condensed  in  wood  towers 
about  1  foot  square  and  perhaps  20  feet  high,  through  which 
a  spray  of  water  is  dropped.  The  fumes  pass  up  and  down 
through  a  series  of  some  six  towers.  The  plant  was  not  in 
operation  on  account  of  shortage  of  sulphuric  acid,  at  the 
time  of  my  visit.  Excellent  results  are  claimed  for  this 
plant. 

Labor  required. — The  tank-room  labor  is  subdivided  as  fol- 
lows: In  addition  to  the  general  foreman,  there  are  three  shifts 
of  three  men  each  who  inspect  the  tanks  for  short  circuits,  clean 
bars,  empty  and  fill  tanks  with  solution,  put  on  and  take  off 
clips,  and  clean  cathodes.  Two  men  are  employed  putting 
cathodes  into  the  depositing  tanks.  Three  men  clean  the 
anode  scrap;  two  men  clean  tanks;  one  man  runs  the  crane; 
one  man  attends  to  the  changing  of  the  electric  connections 
and  the  siphons;  three  men  hang  sheets;  two  boys  clean 
cathode  cross-bars;  one  man  makes  sheets;  one  man  for 
night  watchman  who  also  makes  some  sheets;  one  man  on 
the  day  shift  and  one  man  on  the  evening  shift  are  employed 
in  washing  slime  free  from  lead-depositing  electrolyte,  and 
two  men  follow  the  crane,  making  one  foreman  and  twenty- 
nine  men  in  all.  The  wages  are  34.5  cents  per  hour  and  the 


APPENDIX.  327 

men  get  out  45  to  50  tons  at  the  present  time  in  about  6.5 
hours.  I  am  informed  both  by  the  superintendent  and  the 
foreman  that  the  same  crew  could  handle  the  full  80  tons  in 
eight  hours,  with  two  or  three  additional  men.  The  reason 
for  this  is  that  there  is  not  sufficient  work  for  the  men  at  pres- 
ent, and  the  men  are  probably  allowed  to  waste  a  good  deal 
of  time,  as  they  are  paid  by  the  hour,  and  labor  is  so  scarce 
that  they  would  leave  if  they  only  got  five  hours  work  a 
day. 

With  a  production  of  50  tons  per  day  the  labor  cost  is  evi- 
dently about  $1.40  per  ton  at  present,  and  with  80  tons  pro- 
duced- per  day,  it  would  be  about  $1.17  per  ton.  With  labor 
at  25  cents  per  hour  it  would  evidently  be  for  80  tons  per 
day  about  $0.85  per  ton.  Eventually  the  plant  will  probably 
have  an  anode-wiping  rig  that  will  handle  a  tank-load  of  scrap 
.at  a  time,  and  if  the  plant  had  more  slime  washing  tanks,  or 
If  they  were  larger,  one  man  could  easily  do  the  work  that 
now  takes  two  men,  which  would  reduce  the  cost  per  ton  at 
Trail  on  the  80-ton  scale  by  about  10  cents. 

The  labor  loading  and  unloading  lead  and  bullion  and 
firing  and  melting  takes,  in  addition  to  the  general  foreman 
six  men  casting  anodes  (divided  into  two  shifts)  and  six  men 
on  one  shift  casting  and  loading  lead,  and  five  men  unload- 
ing bullion  and  shifting  anodes,  while  one  man  fires  the  pots 
and  dumps  cathodes  in  the  daytime.  This  includes  the  sam- 
pling of  the  bullion  and  the  remelting  of  the  anode  scrap  and 
skimming  the  pots.  This  force  is  fully  employed  to  handle 
50  tons  on  an  eight-hour  shift.  The  wages  are  the  same  as 
for  the  tank-room  force,  so  the  labor  cost  with  the  present 
arrangement  of  plant  is  evidently  about  $1.00  per  ton  refined, 
including  loading  and  unloading,  firing,  sampling,  and  wheel- 


328  LEAD  REFINING    BY   ELECTROLYSIS. 

ing  lead  and  bullion  about  the  refinery.  Certain  reductions 
in  this  item  are  planned.  It  should  be  remarked  that  the 
refinery  has  no  electric  or  other  power  traction  system  for 
moving  lead  around,  and  there  is  a  chance  to  make  a  saving 
there.  Forty  pounds  of  coal  are  consumed  per  ton  of  lead 
melted.  The  refinery  will  probably  ultimately  receive  bul- 
lion in  the  form  of  anodes  instead  of  pigs,  which  will  save 
quite  a  little  expense.  The  repair  item  is  very  small  with  the 
steel  pots  in  use,  which  last  for  a  very  long  time.  There  are 
employed  at  the  refinery  two  carpenters  and  one  machinist, 
for  repairs  and  improvements.  There  are  two  80-H.P. 
boilers  which  are  fired  by  the  same  man  who  runs  the  elec- 
tric generators,  three  in  all  for  the  three  shifts. 

In  the  slime  plant  there  are  employed  one  foreman;  two 
men  boiling  slime  with  sodium-sulphide  solution;  three  men 
on  the  antimony  depositing  tanks,  who  also  take  care  of  the 
lead  fluosilicate-solution  evaporators;  two  men  drying  and 
handling  slime;  three  furnacemen  on  the  roasting  furnaces; 
and  one  man  in  the  copper-sulphate  crystallizing  plant,  twelve 
men  altogether.  I  did  not  make  any  inquiry  about  the  part- 
ing process  and  operation,  as  that  is  such  a  well-known  process 
anyway. 

The  superintendent's  assistant  keeps  the  records  of  opera- 
tion, shipments,  etc. 

At  the  time  of  my  visit  the  electrolyte  in  the  lead  deposit- 
ing tanks  was  rather  weaker  than  usual  owing  to  a  scarcity 
of  sulphuric  acid  for  making  fluosilicic  acid,  and  contained 
about  5  gr.  lead  and  10  gr.  SiF6  per  100  cc.  I  was  informed 
that  the  greatest  economy  at  Trail,  after  taking  into  con- 
sideration everything,  as  power,  acid  loss,  etc.,  was  reached 
with  a  solution  containing  about  12  gr.  SiF6  per  100  c.c 


APPENDIX. 


329 


It  would  be  expected  that  at  Trail,  with  expensive  acid  and 
not  very  expensive  power,  the  greatest  economy  would  be 
achieved  by  economizing  in  acid  at  the  expense  of  some  power. 
The  acid  loss  for  the  proceeding  two  months  had  been  7  and 
6  Ibs.  of  SiF6  per  ton  lead  respectively.  Mr.  Miller  in- 
formed me  that  he  thought  it  averaged  about  8  Ibs.  when 
the  plant  was  running  full.  The  circulation  is  maintained 
at  about  5  to  7  gallons  of  solution  per  minute  for  each  tank. 
The  current  efficiency  averages  about  88%.  The  e.m.f.  per 
tank  is  about  0.4  volts. 

The  daily  report  is  made  out  on  the  form  shown: 


TRAIL  SMELTER 
LEAD  REFINERY  REPORT. 


May  31,  1907. 


TANK    ROOM. 


Pig  Lead  Produced Ibs.         Last  10  Days 465.36  tons 

Pig  Lead  Produced  this  Month  to  Date 1527. 51  tons 

Pipe 34         tons 


[Acid  9.2     10.1     Pet. 

Electrolyte     j  Lead  4.4      5.0     Pet. 

Sp.  Gr.  1.13     1.16 

[Temp.  34°  C. 


Average  Amperes    .  .  3066 . 6 

Average  Volts 72 . 2 

H.P 296.5 

Time  Running 24         hours 


First  Crop.                              Second  Crop. 
Tank  Efficiency  95.7     Last  10  Days     98.3     Last    Month  86.3 
Lead  per  K.W.  Hour  20.2       "     10     "        20.7       " 

No.  of 
Tanks 
Charged. 

Weight  Anodes. 

Weight  Cathodes  . 

Weight  Scrap. 

Pet.  Scrap. 

Starting  Sheets,  Made  No.         378         Day  Shift         210 


Night  Shift 


330  LEAD  REFINING   BY  ELECTROLYSIS. 


MELTING-ROOM. 


Refined  Lead  Shipped 


'Lot  No.         1116        967         Pigs  87,915      Ibs. 

Lot  No.         1117         435         Pigs  40,001      Ibs. 


1402         Total         127,916      Ibs. 
Refined  Lead  on  Hand 


| Pigs Ibs. 

Lead  Pipe Ibs. 

Cathodes ibs. 

iTotal .  .Ibs. 


Bullion  Received,  Lot  No Bars Ibs. 

Bullion  on  Hand,  Trail Bars H.  M.  Bars 

No.  Anodes  Made  Night  Shift,     150     Day  Shift,     190  Total 

REMARKS.  . . 


N.  B. — Lead  produced  does  not  include  pipe  or  dross. 

Plates    8  to  13  show   interior   and    exterior   views  of  the 
refinery. 


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APPENDIX  II. 

LEAD-REFINING  PLANT  OF  THE  UNITED  STATES  METALS 
REFINING  COMPANY  AT  GRASSELLI,  LAKE  COUNTY, 
INDIANA. 

THE  principal  buildings  are  an  office  building,  tank  and 
melting  building,  72  feet  by  360  feet  for  the  depositing  tanks 
and  melting  furnaces,  a  power  plant  at  one  end  of  the  large 
building,  and  a  hydrofluoric  and  fluosilicic  acid  building. 
The  slime-washing  machinery  and  evaporators  are  located 
in  separate  small  buildings. 

The  power  plant  has  two  boilers,  only  one  of  which  is  re- 
quired at  a  time.  The  fuel  is  local  bituminous  coal  of  fair 
quality.  One  cross-compound  Nordberg  engine  drives  a 
Crocker-Wheeler  electrolytic  generator,  having  its  maximum 
efficiency  at  60  volts  and  4,500  amperes  and  capable  of  carry- 
ing considerable  overload.  The  same  engine  drives  by  belting 
a  small  generator  for  power  and  lighting  purposes.  A  smaller 
double-expansion  Nordberg  engine  drives  a  Westinghouse 
110-K.W.,  110- volt,  1000-ampere  dynamo  which  can  be  used 
for  power  and  lighting  purposes,  and  has  very  considerable 
reserve  capacity.  The  power  plant  and  the  tank  and  melt- 
ing plant  are  in  handsome  substantial  brick  buildings. 

The  tanks  occupy  the  rear  end  of  the  large  building  near 
the f power  plant.  The  tank  arrangement  follows  the  Walker 

343 


344  LEAD  REFINING   BY   ELECTROLYSIS. 

system  as  used  in  copper  refineries,  but  the  number  of  tanks 
per  block  is  four  only  instead  of  the  large  number  used  for 
copper. 

Each  tank  takes  26  anodes  (for  size  of  tanks,  etc..  see 
page  214)  and  27  cathodes  of  sheet  lead  weighing  about  18 
Ibs.  each.  The  cathodes  are  cast  of  the  form  shown  in 
Fig.  57,  and  the  sheets  are  hung  over  the  cathode-bars,  which 
are  of  copper  about  fXlJ  inches  in  cross-section,  on  a  special 
table  provided  for  the  purpose.  A  hole  is  punched  through 
the  sheet  and  the  overlapping  strips,  and  the  burr  produced 
hammered  out,  giving  a  satisfactory  hold,  and  a  double  thick- 
ness of  lead  at  the  solution  line,  which  latter  is  a  help  in  that 
there  is  little  or  no  chance  of  the  solution  cutting  through 
the  cathode  at  the  surface,  during  the  time  the  sheet  remains 
in  the  tank. 

The  tanks  are  lined  with  an  asphaltum  mixture.  Great 
carf!  is  required  in  getting  a  proper  mixture;  one  that  will 
not  soften  at  the  temperature  of  the  electrolyte  and  will  not 
crack  in  cold  weather  if  the  tanks  are  empty. 

Electric  motor-driven  centrifugal  pumps  raise  the  solution 
from  the  pump-tanks  beneath  the  level  of  the  depositing-tanks 
to  the  feed-tanks  at  a  level  higher  than  the  depositing-tanks, 
leaving  the  rest  of  the  flow  through  the  tanks  to  be  accom- 
plished by  gravity.  The  solution  circulates  through  two  tanks 
only  before  it  again  flows  down  to  the  storage  and  pump 
tanks. 

The  tanks  are  supported  on  concrete  piers,  which  are  well 
asphalted.  The  ground  under  the  tanks  slopes  to  sumps  and 
is  also  well  asphalted. 

Two  electric  travelling  cranes,  72-foot  span,  capacity  10 
tons,  command  the  entire  tank  and  melting  space.  One  crane 


APPENDIX.  345 

could  probably  do  all  the  work  quite  well  if  the  other  should 
be  out  of  order. 

Tapering  tank  bus-bars  are  used  to  save  in  copper.  All 
electrodes  are  supported  on  small  triangular  copper  rods  fas- 
tened to  the  bus-bars  on  the  outside  of  each  block  of  tanks, 
while  for  the  intermediate  supports  the  triangular  pieces 
suffice. 

The  bullion  comes  to  the  refinery  already  cast  in  anodes, 
from  the  United  States  Smelter  near  Salt  Lake  City.  They 
are  unloaded  from  the  box-cars  and  sampled  by  punching, 
with  the  help  of  a  chain  block  and  a  temporary  track  run 
into  each  car,  at  a  labor  cost  of  probably  about  6  cents  per 
ton.  The  anodes  are  2  feet  wide  and  3  feet  deep  and  weigh 
about  450  Ibs.  each. 

There  are  two  melting  kettles  at  one  end  of  the  main 
building  nearest  the  railroad  track,  one  of  which  is  used  for 
melting  refined  lead  and  the  other  for  making  fresh  anodes 
from  the  anode  scrap.  The  pots  are  at  quite  an  elevation 
above  the  floor,  so  that  the  lead  may  be  siphoned  out,  though 
it  is  the  intention  to  use  a  centrifugal  pump  as  at  Trail.  The 
lead  is  molded  in  the  usual  manner  and  goes  into  the  market 
marked  " electrolytic."  The  bullion  is  molded  into  ten  flat 
open  molds,  and  removed  with  an  air  hoist  running  on  an 
overhead  track. 

The  washing  of  the  cathodes  is  now  done  with  a  spray, 
though  the  method  in  use  at  Trail  will  probably  be  adopted, 
as  it  is  perhaps  a  little  quicker.  The  anode  scrap  with  attached 
slime  is  hung  by  the  tank-load  in  a  tank  of  about  the  same 
size  as  the  electrolytic  tanks,  and  a  gang  of  five  men  with  scrub- 
bing brushes  attached  to  poles  about  six  feet  long,  reach  in 
between  the  anodes  and  wipe  off  the  slime  into  the  solution 


346  LEAD   REFINING   BY   ELECTROLYSIS. 

or  washwater  in  the  tank.  The  crane  then  picks  up  the 
load,  when  it  is  washed  with  a  spray  of  water  and  is  then 
carried  to  the  pot,  and  lowered  part  way  in.  When  the  crane 
travels  off  the  side  of  the  pot  draws  the  cathodes  off  the  lift- 
ing rack,  and  the  cathodes  fall  in.  The  crane  has  two  lifting 
ropes,  one  at  each  end  of  the  lifting  rack,  otherwise  this 
method  would  not  be  practicable. 

The  slime  removed  from  the  anode  scrap,  and  that  col- 
lected from  the  bottoms  of  the  electrolytic  tanks  is  piped 
to  a  separate  building.  Part  is  pumped  into  a  large  iron  filter- 
press  until  the  press  is  filled  up,  when  an  air  blast  is  turned 
in  to  get  as  much  of  the  strong  solution  out  as  possible.  The 
slime  is  then  washed  with  cold  water,  until  the  solution 
running  out  is  reduced  to  2°  Beaume,  when  the  air  blast  is 
again  turned  in  to  diy  the  slime.  The  rest  of  the  slime 
is  washed  in  two  centrifugal  machines  with  copper  baskets. 
The  slime  is  next  dumped  into  'iron  drying  pans  heated  by 
a  fire  (steam  drying  is  too  slow),  and  when  the  moisture  is 
reduced  from  about  40%  as  it  comes  from  the  filtering  machines 
to  10  or  20%,  it  is  barrelled  and  shipped  to  the  company's 
refining-plant  at  Chrome,  N.  J.,  for  further  treatment. 

The  strong  solutions  and  washwaters  from  the  filtering 
plant  are  probably  returned  to  the  electrolytic  tanks,  while  the 
weaker  are  evaporated.  The  evaporation  is  partly  carried 
out  in  wood  tanks  as  at  Trail,  and  also  in  a  large  circular 
tank  of  hard  lead,  the  latter  being  decidedly  the  best. 

The  lead-depositing  electrolyte  at  the  time  of  my  visit 
contained  about  6  grams  of  lead  and  9  gr.  of  SiF6  per 
100  cc.  The  temperature  was  about  32°  C.  and  the  volts 
per  tank  about  .45.  The  solution  will  undoubtedly  be 
strengthened  up  later. 


APPENDIX.  347 

The  acid-making  plant  is  very  complete.  The  fluorspar, 
slightly  in  excess,  is  mixed  with  not  too  strong  sulphuric  acid 
and  distilled,  and  the  hydrofluoric  acid  produced  is  saturated 
with  silica  in  tanks  with  mechanical  agitators.  The  results 
are  excellent,  and  the  building  is  usually  free  from  acid 
funtes. 

Plates  14,  15,  and  16  are  views  of  the  works. 


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APPENDIX  III. 

TREATMENT   OF   LEAD   REFINERY   SLIME   WITH   SOLUTION   OF 
FERRIC  FLUOSILICATE  AND  HYDROFLUORIC  ACID. 

THE  treatment  of  lead  refinery  slime  is  on  a  fairly  satis- 
factory basis,  by  methods  discussed  in  Chapter  II,  but  in  the 
endeavor  to  carry  the  electroyltic  treatment  to  greater  per- 
fection I  made  experiments  in  my  laboratory,  which  I  shall 
describe  below. 

The  experimental  operation  was  on  a  scale  corresponding 
to  the  treatment  of  the  slime  from  one  ton  of  lead  bullion 
per  day.  The  experimental  plant  was  run  continually  twenty- 
four  hours  each  day  in  charge  of  two  shifts,  while  daily  analyses 
of  important  products  were  made,  to  follow  the  operation  as 
closely  as  possible. 

There  were  so  many  difficulties  to  contend  with,  prin- 
cipally with  the  apparatus,  that  after  running  about  a  week, 
I  was  obliged  to  shut  down  and  make  changes.  After 
starting  up  again  the  plant  was  operated  continuously  for 
two  weeks,  until  the  supply  of  slime  on  hand  was  practically 
used  up. 

During  the  middle  of  the  second  run  the  supply  of  lead 
electrodes  was  used  up,  and  the  operating  force  was  too  busy 
to  make  more,  so  that  it  was  a  case  of  shutting  down  and 
beginning  over  again,  or  changing.  The  deposition  of  the  sepa- 
rate metals  was  not  being  done  well,  and  it  seemed  impossible 

355 


356  LEAD  REFINING  BY  ELECTROLYSIS. 

to  do  it,  at  least  with  the  arrangement  of  plant.  Partly  under 
the  force  of  necessity,  I  introduced  a  change  in  the  process  at 
this  time,  that  turned  out  in  a  very  gratifying  way. 

The  scale  of  operation  and  the  desire  to  operate  the  plant 
continuously  afforded  a  better  test  of  what  could  be  done  on  a 
commercial  scale,  than  smaller  laboratory  tests  could  have 
possibly  given. 

The  process  used  was  referred  to  in  Chapter  II,  page  92, 
and  is  similar  in  some  respects  to  processes  mentioned  on 
pages  119-123  and  134-137.  In  a  general  way  the  process 
consists  in  attacking  the  fresh  unoxidized  wet  slime  with  a 
solution  of  ferric  fluosilicate  and  hydrofluoric  acid  which  re- 
moves over  99%  of  the  arsenic  and  copper,  90%  or  more  of 
the  antimony,  and  nearly  90%  of  the  lead.  Originally  it  was 
intended  to  remove  from  the  resulting  solution,  first  the  copper 
as  cathode  metal,  while  antimony  anodes  dissolved,  thus 
substituting  antimony  for  copper.  Next  the  antimony  was 
to  be  deposited  using  lead  anodes  which  dissolve,  so  that  lead 
takes  the  place  of  antimony  in  the  solution.  After  this  the 
arsenic  was  to  be  plated  out  as  a  lead-arsenic  alloy,  while  lead 
anodes  were  also  used  in  this  case,  thus  substituting  lead  for 
arsenic.  The  solution  now  containing  only  lead  and  ferrous 
fluosilicates  was  to  be  electrolyzed  for  metallic  lead  and  ferric 
fluosilicate,  the  latter  to  be  used  over  again  in  the  same  way 
as  before.  Of  course  the  different  electrolytic  steps  were  to 
be  performed  in  separate  sets  of  tanks  through  which  the 
solution  flowed  in  series. 

Later,  the  electrolytic  deposition  of  copper,  antimony,  and 
lead-arsenic  was  given  up  and  the  metals  cemented  out  in 
layers  of  different  composition  by  causing  the  solution  to  flow 
through  the  lead  product  obtained  in  the  ferric-iron  producing 


APPENDIX.  357 

tank.     This   gave   a   separation,   although  the   antimony   and 
arsenic  were  recovered  together. 

The  use  of  hydrofluoric  acid  in  the  solution  is  important, 
because  without  it  only  a  little  antimony  could  be  dissolved. 
If  hydrofluoric  acid  only  was  used  lead  could  not  be  extracted. 
By  the  addition  of  hydrofluoric  acid  to  the  solution  within* 
certain  limits,  the  extraction  of  the  antimony  may  be  secured, 
without  spoiling  the  lead  extraction. 

The  ferric  fluosilicate-hydrofluoric  acid  seems  to  me  to 
be  probably  the  best  of  all  wet  slime  processes,  because  it 
offers  these  advantages:  A  minimum  of  electrolysis  to  produce 
the  desired  products;  recovery  of  any  lead  refining  solution 
or  any  fluorine  left  in  the  slime  by  incomplete  washing,  or 
decomposition  of  the  lead  depositing  electrolyte;  treatment 
of  wet,  raw,  and  imperfectly  washed  slime;  simplicity;  no 
chance  to  lose  valuable  metals;  elimination  of  arsenic  from 
the  slime-treating  solution;  and  recovery  of  the  arsenic.  Very 
few  of  the  slime  processes  have  any  of  these  advantages. 

Experiments  were  made  to  find  a  suitable  electrolytic 
diaphragm  capable  of  withstanding  solutions  containing  hydro- 
fluoric acid.  With  asbestos  and  earthenware  impossible,  it 
is  not  an  easy  matter  to  produce  a  diaphragm.  Quite  satis- 
factory tests  were  obtained  with  carbon  buttons,  prepared  by 
mixing  powdered  charcoal  with  asphaltum  varnish  and  stamp- 
ing into  buttons  1J  inches  diameter  and  T36  inches  thick,  which 
were  dried  and  baked  gently.  Using  soft  charcoal  and  baking 
below  a  red  heat  the  product  was  electrically  non-conductive, 
and  after  removing  air  under  an  air-pump,  or  boiling  in  a 
solution  of  sodium  nitrate,  gave  a  fair  electrolytic  conduc- 
tivity. 

Preliminary  tests  were   made  on  two  lots  of   lead   slime. 


358 


LEAD  REFINING  BY  ELECTROLYSIS. 


Lot  1  had  been  partially  dried  in  the  usual  course  of  treatment 
and  was  pretty  well  oxidized.  Lot  2  had  been  merely  filter 
pressed,  and  was  practically  non-oxidized.  The  latter  kind 
only  is  suitable  for  the  ferric  fluosilicate-hydrofluoric  acid 
process.  The  analyses  are  given  in  Table  121.  The  last  anal- 
ysis given  for  Lot  2  is  the  most  accurate. 

TABLE  121. 


Lot  1. 

Lot.  ; 

l. 

Moisture  

20       % 

47.75% 

Antimony  on  dry  residue  

33.75% 

39.22% 

Copper  on  dry  residue 

1  45% 

2  25% 

2  45% 

Arsenic 

12  60% 

14  10% 

16  00% 

Silver  

12  08% 

16  .  24% 

17  20% 

Bismuth  .  .        

1.60% 

2  60% 

Tellurium  

1  30% 

Selenium  

trace 

Iron 

0  50% 

Lead. 

12  06% 

9  88% 

11  9  % 

Fusol  .  . 

16  00% 

The  amount  of  ferric  iron  required  for  a  given  slime  can  be 
calculated  from  its  composition,  if  the  slime  is  unoxidized,  or 
determined  experimentally.  The  method  of  testing  the  iron- 
reducing  power  consists  in  boiling  with  an  excess  of  ferric- 
sulphate  and  boiling  the  filtrate  with  metallic  copper  until 
all  ferric  iron  is  reduced.  Multiplying  the  amount  of  copper 
dissolved  by  1.76  and  subtracting  the  result  from  the  amount 
of  ferric  iron  used  gives  the  iron  reduction  figure.  Of  Lot  2, 
100  grams  as  dry  slime  reduced  94.5  grams  of  ferric  iron,  which 
shows  practically  no  air  oxidation  to  have  taken  place.  Of 
Lot  1,  100  grams  as  dry  slime  reduces  13.8  grams  ferric  iron, 
showing  approximately  85%  air  oxidation.  This  is  about  the 
usual  figure  for  soft  slime,  dried  in  air. 

A  test  on  100  grams  Lot  1  with  ferric  fluosilicate  and  hydro- 


APPENDIX. 


359 


fluoric  acid  gave  a  25-gram  residue,  containing  Fe  3.5%,  Cu 
none,  Sb  18.5%,  Bi  3.45%,  Pb  9.35%. 


TABLE  122. 


In  Original  Slime 

In  Residue. 

Per  Cciit. 
Dissolved. 

Antimony 

27  grams 

4  .  62  grams 

82.9% 

Copper  
Arsenic       

1  .  16  grams 
10.1 

none 

100.0 

Lead  

10.1 

2.34 

76.5 

Bismuth 

1  28 

0  86 

37  8 

Six  hundred  and  fifty  grams  of  Lot  1  (520  grams  dry  weight), 
leached  with  a  fluosilicate-fluoride  solution  containing  42  grams 
ferric  iron  gave  a  159-gram  residue  containing  39.8%  silver, 
10.5%  antimony,  no  copper,  24%  lead,  no  arsenic,  3.41% 
bismuth.  This  shows  an  extraction  of  90%  of  the  antimony; 
all  copper  and  arsenic;  42%  of  the  lead,  and  40%  of  the  bis- 
muth. 

The  poor  extraction  of  lead  was  due  to  the  solution  con- 
taining too  much  HF,  so  that  lead  fluoride  was  formed  and 
remained  undissolved.  The  percentage  of  bismuth  extracted 
is  not  of  great  importance,  as  the  process  recovers  both  un- 
dissolved and.  dissolved  bismuth.  The  solubility  of  bismuth 
in  these  solutions  was  approximately  1  gram  per  liter. 

No  further  preliminary  tests  were  thought  necessary  on 
Lot  2. 

The  apparatus  to  be  used  consisted  of  a  series  of  tanks. 
In  the  first  the  solution  from  the  slime  is  elect roly zed  with  a 
low  current  density  of  about  five  amperes  per  square  foot, 
using  copper  cathodes  and  antimony  anodes.  The  antimony 
dissolves  at  the  anodes  while  copper  and  presumably  bismuth 
deposit.  The  solution  is  supposed  to  flow  from  the  tanks 


360 


LEAD  REFINING  BY  ELECTROLYSIS. 


practically  free  from  copper  and  bismuth.  The  next  series 
of  tanks  was  much  larger  and  contained  lead  anodes  and  copper 
cathodes;  lead  dissolving  and  antimony  depositing,  with  a 
current  density  of  about  12  amperes  per  square  foot,  which 
was  found  later  to  be  decidedly  too  high,  so  more  tanks  were 
used  and  the  current  density  reduced  to  7  amperes.  Leaving 
these  tanks,  the  solution  containing  a  little  antimony  passes 
through  another  somewhat  smaller  set,  having  lead  anodes 
and  cathodes.  In  the  first  of  this  set  lead  and  antimony  with 
some  arsenic,  and  later  lead  and  arsenic,  and  finally  nearly 
pure  lead  deposit,  or  at  least  were  expected  to.  The  anodes 
in  the  antimony-depositing  tanks  contained  about  0.6%  anti- 
mony, and  those  in  the  arsenic-depositing  tanks  were  of  prac- 
tically pure  lead.  The  dimensions  of  these  tanks  are  given 
in  Table  123. 

TABLE  123. 


No. 

Length, 
Inches. 

Depth, 
Inches. 

Breadth, 
Inches. 

Cathodes, 
Inches. 

Anodes, 
Inches. 

Copper  tanks  

6 

6 

8 

7 

6X6 

6X   7 

Antimony  tanks  .... 
Arsenic  tanks  

3 
3 

11 
10 

17 
16 

14 
12 

13*X16 
10JX12J 

10X13* 

10X13* 

All  tanks  were  fitted  with  independent  agitators  capable 
of  maintaining  a  good  circulation,  which  is  very  necessary  with 
this  process,  because  the  solutions,  except  in  the  ferric  iron 
tank,  are  very  dilute  with  respect  to  the  metals  being  deposited. 

The  diaphragms  for  the  ferric-iron  tank  were  prepared  by 
stamping  a  charcoal  and  asphaltum  mixture  into  buttons, 
1J  inches  in  diameter,  and  about  ^-inch  thick,  drying  and 
baking  below  a  red  heat.  About  2150  of  these  were  inserted 
and  made  fast  with  thick  asphaltum  varnish  in  holes  bored  in 


APPENDIX.  361 

the  sides  of  five  wooden  boxes,  which  were  to  form  the  anolyte 
compartments.  These  boxes  were  made  of  f-inch  wood,  and 
were  3  inches  wide  by  30J  inches  long  by  22  inches  deep  inside. 
Before  inserting  the  carbon  buttons  they  were  boiled  in  sodium 
nitrate  solution  to  drive  out  the  air  and  wet  the  buttons,  so 
that  they  would  finally  become  wetted  through  when  elec- 
trolyte was  added  to  the  tank.  The  buttons  also  expanded  a 
little  by  this  treatment.  The  space  occupied  by  the  buttons 
on  each  side  of  each  box  was  about  21J  inches  by  29J  inches. 
As  215  buttons  had  an  area  of  264  square  inches,  the  current 
density  in  the  buttons  averages  about  2.5  times  higher  than 
the  anode  and  cathode  current  density  and  approximated 
20  amperes  per  square  foot. 

Five  of  the  anolyte  boxes  were  spaced  with  distance  frames, 
about  3J  inches  apart  in  the  clear  between  the  boxes,  in  an 
asphalted  wooden  tank  with  an  internal  length  of  42  inches, 
width  35  inches,  and  depth  24  inches.  The  whole  was  driven 
tightly  together  with  wedges  inside  the  tanks  at  one  end,  while 
the  tank  was  securely  braced  outside  to  prevent  its  being 
strained  by  the  pressure  developed  by  the  wedges. 

The  anodes  consisted  of  five  sets  of  Acheson  graphite  rods, 
one  inch  in  diameter  and  24  inches  long,  cast  in  lead  at  the 
top  and  carried  by  reciprocating  beams  at  the  sides  of  the  tank. 
The  total  motion  was  f  inch.  There  were  19  anodes  to  the 
frame,  spaced  with  1J  inches  centres.  The  actual  anode  sur- 
face was  about  4%  greater  than  would  be  presented  by  a  plane 
of  the  same  overall  measurements.  The  total  anode  area 
exposed  was  approximately  41.5  square  feet.  The  six  cathodes 
were  of  sheet  lead  21X28  inches  with  an  exposed  total  area 
of  about  41  square  feet.  With  a  current  of  330  amperes,  this 
corresponds  to  a  current  density  of  about  8  amperes  per  square 


362  LEAD  REFINING  BY  ELECTROLYSIS. 

foot.  Provision  was  made  to  keep  all  the  catholyte  and 
anolyte  in  good  circulation  through  the  various  respective 
compartments.  The  circulating  apparatus  adopted  did  not 
work  well  at  all,  unfortunately,  with  the  result  that  the  solu- 
tion in  some  of  the  anolyte  boxes  contained  no  remaining 
ferrous  iron  for  a  large  part  of  the  time,  and  the  anodes  after 
the  runs  were  over  were  found  to  be  considerably  attacked 
in  those  places,  although  in  other  places,  even  where  as  much 
current  was  used,  there  was  no  evidence  of  corrosion. 

The  total  cubic  capacity  of  the  electrolytic  tanks,  taking 
account  of  space  occupied  by  electrodes  and  diaphragms,  was 
about  25  cubic  feet,  while,  when  all  tanks  but  the  iron  tank 
were  cut  out,  the  capacity  approximated  15  cubic  feet. 

The  solution  was  made  up  originally  by  first  dissolving  scrap 
wrought  iron  in  fluosilicic  acid,  and  then  treating  70  Ibs.  of 
oxidized  slime  of  Lot  1  with  a  part  of  the  solution.  The  solu- 
tions were  then  mixed  together  for  the  tanks  and  contained 
12.4  grams  SiF6,  0.1  gram  copper,  2.55  grams  iron,  1  to  2 
grams  HF,  and  0.86  grams  antimony  per  100  c.c. 

The  treatment  of  the  slime  of  Lot  1  by  SiF6  and  HF  did 
not  give  as  high  an  extraction  as  was  expected  from  the  tests 
made  previously.  A  possible  explanation  is  that  the  top  of 
the  barrel  from  which  the  slime  was  taken,  differed  in  oxida- 
tion from  the  middle  plane  from  which  the  sample  was  taken. 
A  content  of  2%  or  more  of  antimony  was  desired  and  had  been 
expected. 

The  total  amount  of  the  solution  used  was  about  900 
liters. 

The  slime  treatment  so  far  was  not  successful,  but  the 
solution  was  most  easily  prepared  in  that  way,  and  that  was 
really  the  reason  this  particular  method  was  used. 


APPENDIX.  363 

The  solution  was  fed  first  to  the  copper-depositing  tanks, 
and  the  others  were  gradually  brought  into  action  as  they 
filled  up. 

The  electrical  conditions  were  about  as  follows,  Table  124: 

TABLE  124. 

Average  Volts.  Average  Current  Density. 

Copper  tanks,  0 . 17  5  amps,  per  sq.  ft. 

Antimony  tanks,  0 .45,  normally  rose  however  to  2  volts 

at  times,  7.4  "  "  "  " 

Arsenic  tanks,  0 . 45,  normally  rose  however  to  2  volts 

at  times,  1.7      "       "    "    " 

The  antimony  anodes  in  the  copper  tanks  dissolved  regularly 
and  evenly.  The  lead  anodes  in  the  antimony  tanks  dissolved 
without  difficulty,  but  lead  fluoride  formed  during  the  first 
run  in  patches  on  the  surface,  and  collected  as  a  white  mud  in 
the  bottoms  of  the  tanks.  The  lead  anodes  in  the  arsenic 
tanks  of  practically  pure  lead  did  not  dissolve  well  at  first. 
The  surface  was  quite  rapidly  covered  with  an  insulating  layer 
containing  lead  fluoride.  These  were  then  replaced  with 
anodes  containing  about  2%  of  antimony,  with  the  idea  that 
the  anode  slime  of  antimony  would  act  as  a  diaphragm  and 
keep  the  HF  in  the  solution  away  from  the  anode  surface. 
The  anodes  dissolved  better  thereafter.  The  explanation  is, 
that  the  current'  is  principally  carried  by  the  SiF6  ion,  the 
formation  of  lead  fluoride  being  largely  a  secondary  reaction 
between  the  PbSiF6  formed,  and  the  HF. 

The  formation  of  lead  fluoride  in  the  tanks  is  not  really 
necessary  in  the  process,  and  did  not  occur  afterward,  but  in 
the  first  part  of  the  run  the  solution  contained  too  much  HF, 
and  quite  a  little  white  lead  had  to  be  added  to  remove  the 
excess. 


364  LEAD  REFINING  BY  ELECTROLYSIS. 

The  lead  fluoride  could  be  worked  up  by  adding  it  to  a 
batch  of  slime,  when  a  reaction  occurs  as  follows : 

2Sb  +  3Fe2(SiFe6)  3  +  3PbF2 = 2SbF3  +  6FeSiF6 + 3PbSiF6. 

The  copper  tanks  took  altogether  6  to  16  amperes,  arranged 
in  two  series,  or  3  to  8  amperes  per  tank,  with  a  current  density 
of  3  to  8  amperes  per  square  foot,  and  voltage  of  0.2  to  0.24 
with  6  amperes  per  square  foot. 

The  antimony-depositing  tanks  took  60  to  150  amperes  for 
the  three  tanks,  or  a  current  density  of  about  5  to  13  amperes 
per  square  foot,  with  normal  voltage  of  0.25  to  0.6.  The  de- 
posited metal  was  of  various  kinds,  and  no  pure  antimony  was 
produced.  The  voltage  rose  much  higher  at  times,  and  probably 
oxidized  some  antimony  to  the  irreducible  SbF  . 

The  " arsenic"  tanks  were  operated  with  10  to  100  amperes, 
averaging  about  30,  or  a  current  density  of  1  to  10  amperes 
per  square  foot.  The  voltage  ranged  from  0.5  to  1.5. 

The  large  ferric-iron  producing-tank  had  an  extremely  high 
resistance  at  first,  until  the  solution  had  penetrated  the  pores 
of  the  carbon.  At  the  end  of  the  run  the  temperature  had 
risen  to  36°  C.  and  the  current  rose  to  335  amperes,  with  2.5 
volts. 

No  difficulty  was  experienced  with  polarization  at  the 
anodes,  provided  they  were  kept  moving  back  and  forth  by 
the  mechanism  provided  therefor.  Otherwise  the  tank  would 
polarize  in  a  minute  or  two,  and  the  voltage  would  show  an 
increase  of  from  0.6  to  0.8  volts.  The  counter  electromotive 
force  of  the  cell  determined  by  opening  the  circuit  and  reading 
the  voltmeter  was  about  1  volt.  No  difficulty  with  silica 
depositing  on  the  anodes  and  causing  polarization  and  gassing 
was  experienced  with  this  process  as  with  the  ferric-sulphate 


APPENDIX.  365 

process,  and  this  could  not  very  well  happen,  because  the 
solution  contained  free  hydrofluoric  acid,  which  would,  of 
course,  keep  silica  in  solution. 

Most  trouble  was  caused  by  the  carbon  buttons  loosening 
and  dropping  out  in  the  tank.  Part  at  least  of  this  trouble 
was  caused  by  faulty  setting  of  the  buttons.  Some  had  been 
put  in  without  any  cementing  material  at  all.  The  leaking 
holes  were  located  and  corked  up,  but  still  the  efficiency  was 
low,  and  at  times  the  mixing  of  anolyte  and  catholyte  was  so 
rapid  that  the  tank  actually  showed  a  loss  of  effect.  By  sam- 
pling different  parts  of  the  anolyte  and  titrating  with  per- 
manganate, the  efficiency  could  be  determined.  The  highest 
obtained  for  the  whole  tank  was  56%,  although  three  of  the 
five  anolyte  boxes  showed  100%  at  one  time. 

The  lead  deposited  at  the  cathode  was  of  a  peculiar  char- 
acter. It  was  not  solid,  nor  apparently  crystalline,  even  under 
the  microscope.  It  did  not  show  any  tendency  to  tree  out, 
and  make  short  circuits,  but  covered  the  cathodes  in  a  felted 
layer,  which  would  drop  off  when  the  layer  became  too  thick, 
in  say,  twenty-four  hours.  The  same  kind  of  a  lead  deposit 
is  that  obtained  from  other  solutions  containing  a  fraction  of 
a  per  cent  of  arsenic  and  antimony.  As  the  lead  was  not  in 
satisfactory  shape  to  either  build  up  a  solid  cathode  or  for 
melting,  a  rolling  rig  to  pack  the  deposit  down  was  made. 
This  was  not  tried  until  the  second  run  and  then  only  for  a 
time. 

The  anodes  were  given  about  50  complete  vibrations  per 
minute  to  keep  them  from  polarizing.  A  good  deal  of  the 
time  there  was  no  motion  as  the  motor  driving  the  anode 
frame  was  difficult  to  regulate  with  the  means  at  hand. 

The  difference  in  specific  gravity  of  catholyte  and  anolyte 


366  LEAD  REFINING  BY  ELECTROLYSIS. 

was  only  slight,  during  this  run,  but  it  seemed  to  increase  as 
the  percentage  of  lead  in  the  anolyte  diminished.  Catholyte 
with  28  grams  ferrous  iron  per  liter,  had  a  density  of  1.132 
at  36°,  while  anolyte  with  7.3  grams  ferrous  iron  had  a  density 
of  1.144. 

Some  slime  of  Lot  2  was  treated  during  this  run  by  anolyte 
taken  from  the  ferric-iron  tank.  The  slime  was  stirred  up  in 
a  barrel  with  a  slighter  excess  of  ferric  iron,  calculated  as 
follows : 

1  part  copper       requires  1.76  parts  Fe"' 
1    "    antimony        "        1.4       "        " 
1    "    arsenic  "        2.23     "       " 

1    "    bismuth          "        0.81     " 
1    "    lead  "        0.54     " 

The  solution  after  settling  was  siphoned  off  and  agitated 
with  a  small  quantity  of  fresh  slime  to  reduce  any  ferric  iron 
or  precipitate  any  silver  in  solution.  The  solution  was  then 
settled  and  run  through  a  filter  into  a  tub  which  fed  the  elec- 
trolytic tanks.  The  slime  after  treatment  with  the  solution 
left  only  a  small  volume  of  a  dense  metallic  residue,  of  far  less 
bulk  than  the  slime  treated.  It  filtered  fairly  well  with  cold 
water,  and  washed  rapidly  with  hot  water. 

The  residue  was  analyzed  and  found  to  contain  lead  11.4%, 
antimony  14.1%,  arsenic  1.48%,  Bi  0.54%.  The  silver  by 
solution  in  nitric  acid  and  titration  with  NH4CNS  was  58.3%r 
a  little  less  than  the  actual  amount.  For  quick  determinations 
to  control  the  process  this  method  was  used  however.  Taking 
silver  in  the  original  slime  at  16.2%,  obtained  by  the  same 
method,  and  assuming  that  no  silver  was  dissolved,  the  results 
are  given  in  Table  125. 


APPENDIX 
TABLE  125. 


367 


In  13  Lbs. 
Wet  Slime. 

In  1.9  Lbs. 
Dry  Residue. 

Extracted. 

Antimony    .          

2.67  Ibs. 

0.27  Ibs. 

90% 

Copper    

0.151bs. 

none 

100% 

Arsenic         • 

0.96  Ibs. 

0.03  Ibs. 

97% 

Silver       

1.11  Ibs. 

1.11  Ibs. 

none 

Bismuth                                .    ... 

0.18  Ibs. 

0.01  Ibs. 

94% 

Lead.                                   

0.68  Ibs. 

0  .  22  Ibs. 

68% 

The  solution  from  the  slime  treatment  was  partly  passed 
into  the  series  of  electrolytic  tanks,  but  mostly  stored  and 
used  in  the  second  run. 

The  somewhat  inferior  results  in  extraction  were  probably 
due  in  part  to  the  low  temperature  at  which  the  slime  treat- 
ment was  conducted,  namely,  12°-13°  C.  In  the  following 
run  the  temperature  was  25°-30°  C. 

A  test  was  made  on  one-half  barrelful  of  solution  with  the 
proper  addition  of  slime,  to  see  if  there  was  any  increase  in 
the  percentage  of  SiF6  in  the  solution.  It  had  been  thought 
that  the  slime  contained  in  an  unrecoverable  form  products  of 
the  fluosilicic  acid  used  in  refining  the  lead.  Very  careful 
analyses  before  and  after  adding  the  slime  showed  no  change 
in  the  amount  of  SiF6  present.  Very  little  could  have  been 
in  the  final  residue,  so  that  with  well-washed  slime  there  is 
no  apprecaible  quantity  of  fluosilicic  acid  or  decomposition 
products  left  in  the  slime  from  lead  refining. 

At  the  end  of  the  run  none  of  the  tanks  had  given  satis- 
faction. There  was  difficulty  keeping  the  contacts  in  con- 
dition on  the  copper  tanks,  because  the  electrodes  were  very 
light.  No  pure  copper  was  produced,  and  much  pure  antimony 
had  been  converted  into  impure  metal. 

No  good  antimony  had  been  made  in  the  antimony  tanks, 


368  LEAD  REFINING  BY  ELECTROLYSIS. 

but  the  varying  current  -density  and  composition  and  rate  of 
feed  of  solution  were  so  difficult  to  have  controlled  by  my 
assistants  before  it  was  thoroughly  understood  what  was  re- 
quired, that  anything  different  from  a  collection  of  all  kinds  of 
deposits  on  each  electrode  could  not  have  been  expected. 
The  iron  tank  had  failed  because  of  internal  leaks. 

The  experimental  plant  was  then  shut  down  and  altered 
in  many  respects.  The  contacts  were  improved,  new  and  more 
powerful  stirrers  put  in  each  tank,  and  the  capacity  of  the 
antimony-depositing  tanks  increased  66%. 

The  ferric-iron  tank  was  taken  apart,  and  the  anolyte  boxes 
tested  by  filling  them  with  water,  and  all  poorly  set  buttons 
taken  out.  Even  after  that  fears  were  entertained  lest  the 
wood  should  expand  or  contract  by  wetting  or  drying  and 
loosen  the  buttons.  The  plan  of  mounting  the  buttons  in 
hard  rubber  plates  by  means  of  soft  rubber  rings  cut  from  a 
rubber  tube  surrounding  each  button  was  considered,  but  it  was 
thought  to  require  too  much  time.  To  make  sure  of  the  success- 
ful operation  of  the  tank,  so  that  the  process  itself  could  be 
thoroughly  tested,  each  anolyte  box  was  covered  with  a  double 
layer  of  cotton  duck.  The  duck  was  so  successful  in  with- 
standing the  action  of  the  solution,  that  it  will  undoubtedly 
itself  provide  a  suitable  and  economical  diaphragm  if  the 
tank  is  so  constructed  that  new  sheets  of  duck  may  be  sub- 
stituted every  month,  say,  and  without  its  being  necessary  to 
take  the  tank  itself  apart. 

For  the  second  run,  the  old  solutions  were  analyzed  before 
mixing,  with  results  as  in  Table  126. 


APPENDIX. 
TABLE  126. 


369 


Lead. 

Iron. 

SiFe. 

Antimony. 

Fresh  solution  

0.57 

2.14 

14.5 

Old  catholyte  

1.13 

3.08 

12.8 

0.32 

Old  anolyte  after  adding  slime  

1.04 

3.03 

10  9 

1  46 

Old  solution  from  antimony  tanks  .  .  . 
Old  solution  ready  for  depositing  tanks 

3.18 
1.48 

2.72 
2.96 

12.1 
11.3 

0.65 

0.88 

The  mixed  solution  used  contained  about  2.85%  Fe  and 
12.6%  SiF6  and  was  maintained  at  about  this  strength  through- 
out the  run.  The  amount  of  HF  present  was  not  determined, 
but  was  not  far  from  one  per  cent.  The  solution  was  entirely 
too  weak  for  the  best  results,  and  was  low  in  free  acid,  averaging 
about  1  or  2%  only.  What  acid  was  not  combined  with  ferrous 
iron  was  combined  with  lead,  or  the  whole  was  combined  with 
ferric  iron.  If  the  solution  had  contained  more  free  acid,  the 
power  consumption  on  the  iron  tank  would  have  been  much 
less.  It  is  rather  surprising  that  such  good  results  were  ob- 
tained with  such  a  weak  solution.  It  had  been  intended  to 
work  with  16%  SiF6,  but  one  of  the  barrels  in  which  acid  had 
been  stored  had  leaked  out. 

In  starting  up,  the  first  tanks  to  be  put  in  operation  were 
the  copper-depositing  tanks  and  one  of  the  antimony-deposit- 
ing tanks.  As  the  solution  gradually  filled  the  other  tanks 
the  current  was  increased.  After  twenty-four  hours  the  iron 
tank  at  the  end  contained  4  inches  of  solution.  As  it  filled 
the  current  was  increased,  keeping  the  voltage  practically 
constant  at  3.5  volts.  The  current  reached  160  amperes  after 
about  70  hours  and  the  full  300  amperes  was  not  reached  for 
eight  days. 

The  tank  could  have  taken  the  full  current  earlier,  but 
was  in  series  with  the  antimony  and  lead-arsenic  depositing 


370 


LEAD  REFINING  BY  ELECTROLYSIS. 


tanks,  and  the  current  was  kept  down  in  an  attempt  to  get 
the  desired  pure  antimony  deposition.  At  that  time  the 
other  tanks  had  been  finally  taken  out,  and  thereafter  the 
iron  tank  only  was  operated. 

The  copper-depositing  tanks  did  not  give  good  results  at 
any  time,  partly  because  the  contacts  were  poor,  and  the  cur- 
rent density  on  some  electrodes  was  in  consequence  far  too 
high.  I  scraped  the  deposits  from  two  cathodes,  one  with  a 
heavy  deposit  and  the  other  with  a  light  one.  After  melting 
they  gave  on  analysis  the  figures  in  Table  127. 

TABLE  127. 


Lead. 

Copper. 

Bismuth. 

Antimony. 

Arsenic. 

Heavy  deposit  
Light  deposit  

3-57% 
1.9  % 

4.15% 
10.5  % 

1.0% 
5.1% 

74.6% 
69.6% 

14.2% 
13.7% 

There  were  five  antimony-depositing  tanks  on  this  run, 
instead  of  three  as  before.  The  highest  current  density  used 
was  about  6  amperes  per  square  foot.  Some  of  the  best  look- 
ing deposit  contained  8.15%  lead,  so  it  was  apparent  that  the 
most  vigorous  circulation  and  close  regulation  would  be  neces- 
sary for  the  successful  production  of  antimony. 

The  arsenic-lead  depositing  tanks  gave  nearly  continuously 
a  soft  deposit  of  lead. 

After  a  few  days  running  the  copper  tanks  were  found  to 
be  allowing  copper  to  pass  through  them,  and  they  were  dis- 
connected and  replaced  by  a  box  containing  metal  scraped 
from  the  cathodes  in  the  antimony-depositing  tanks.  This 
box  was  11  inches  by  14  inches  and  the  layer  of  metal  which 
rested  on  a  false  bottom  was  about  3  inches  thick.  The  solu- 
tion ran  through  too  rapidly  when  the  box  was  filled,  and  the 


APPENDIX. 


371 


copper  was  not  all  removed.  From  the  analyses  in  Table  128, 
it  will  be  seen  that  the  lead  in  the  box  dissolved  away  first, 
precipitating  antimony  and  copper,  while  later  the  antimony 
dissolved  and  copper  precipitated. 


TABLE  128. 


Day  of  Run. 

Solution  Fed  to  Copper 
Extractor. 

Solution  Flowing  from  Copper 
Extractor. 

Cu 

Sb 

Pb 

Cu 

Sb 

Pb 

5th  

0.075% 
0.086% 

1.35% 
1.65% 

1.70% 
1.80% 

1.48% 
1.77% 

0.04% 
0.04% 

1.54% 
1-75% 
1-80% 

1.78% 

7th 

8th  . 

9th  

0.044% 

0.01% 

0.012% 
0.017% 

llth  

12th  

13th  . 

Better  results  would  have  been  obtained  if  the  box  had 
been  filled  with  lead  from  the  ferric -iron  tank.  This  would 
have  a  finely  divided  form  and  be  more  active  than  the  more 
solid  metal  that  was  used.  With  an  arrangement  such  that 
the  overflow  of  the  box  had  been  high  enough  to  keep  the  pre- 
cipitating metal  always  flooded,  and  the  flow  of  solution  had 
been  uniform,  instead  of  intermittent,  better  results  would  have 
been  obtained. 

Tests  were  then  made  to  determine  whether  antimony  and 
arsenic  could  be  precipitated  by  lead  in  a  similar  manner. 
The  cathode  lead  in  the  ferric-iron  tank,  which  was  being 
packed  down  on  the  cathodes  by  rolling,  was  tried  in  the  test. 
This  material  was  found  to  analyze  at  two  different  times  as 
follows : 


372  LEAD  REFINING  BY  ELECTROLYSIS. 

TABLE  129. 

Sb .46%  .30% 

As 47%  .29% 

It  consists  of  fine  particles  of  lead  loosely  held  together, 
with  no  crystallization  apparent  under  a  small  microscope. 
It  deposits  in  a  felted  layer  on  the  cathodes  and  for  use  in 
precipitating  was  wiped  from  the  cathodes  by  means  of  a 
trowel  into  a  long  tray  resting  on  top  of  the  tank. 

A  layer  of  this  lead  about  three-fourths  of  an  inch  thick 
was  put  in  a  funnel  and  solution  from  slime  treatment  rapidly 
run  through,  with  results  as  given  in  Table  130. 

TABLE  130. 

Solution.  Filtrate.  Soft  Material  Left  on  Filter 

As 0.44%  0.18%  6.7% 

Sb 1.50%  0.87%  24% 

Pb 2.08%  6.9% 

The  layer  of  precipitating  lead  was  too  thin  and  the  speed 
of  flow  was  rapid,  so  a  complete  extraction  of  antimony  and 
arsenic  was  not  expected.  The  solution  used  contained  some 
pentavalent  antimony,  which  is  not  precipi table. 

After  a  number  of  other  similar  tests  were  made  which 
showed  a  ready  precipitation  of  arsenic  and  antimony  by  the 
cathode  lead,  the  solution  running  from  the  copper  extractor 
described  above,  already  in  use  for  two  or  three  days,  was 
passed  through  a  11-inch  by  14-inch  box  containing  a  layer  of 
cathode  lead  several  inches  thick,  resting  on  a  false  bottom. 
The  solution  running  through  contained  0.07%  As  and  0.44% 
Sb.  The  antimony  in  the  run-off  came  down  with  H^  only 
after  a  long  time  and  with  difficulty,  showing  that  it  was 
present  in  the  solution  as  pentavalent  antimony. 


APPENDIX.  373 

After  some  eighteen  hours  the  solution  running  through: 
began  to  contain  more  antimony,  roughly  determined  by; 
titrating  10  c.c.  with  permanganate  solution,  so  another  smaller 
box  7x7  inches  with  a  layer  of  lead  about  3  inches  thick  was 
put  on  just  above  the  original  box.  All  the  electrolytic  tanks: 
except  the  main  tank  were  emptied  and  their  contents  poured' 
through  with  the  solution  coming  from  the  slime  treatment. 

The  solutions  running  through  the  boxes  were  sampled  every; 
two  hours  for  several  days,  and  the  samples  analyzed  for  iron, 
antimony,  and  arsenic.  It  would  take  space  unnecessarily 
to  give  all  the  results,  but  they  showed  a  very  good  extraction 
of  arsenic,  and  extraction  of  practically  all  the  precipitable 
antimony,  when  sufficient  lead  was  in  the  precipitating  boxes. 

The  solution  still  contained  about  0.6%  of  antimony  m 
the  pentavalent  condition,  a  result  of  either  the  high  voltage 
developed  at  times  in  the  antimony  and  lead-arsenic  tanks, 
or  of  oxidation  in  some  of  the  compartments  of  the  ferric-iron 
tank,  when  the  supply  of  ferrous  iron  was  exhausted  from- 
insufficient  circulation.  I  had  another  unfavorable  condition 
to  contend  with  in  not  having  a  sufficient  stock  of  cathode 
lead  on  hand  to  fairly  fill  the  precipitating  boxes,  as  a  result 
of  which  the  lead  in  the  boxes  was  at  times  practically  ex- 
hausted before  I  had  collected  enough  from  the  tank  to  fill 
them,  while  some  was  wasted  as  we  were  compelled  to 
work.  Practically  the  amount  of  lead  taken  from  the  elec-* 
trolytic  tank  exceeds  the  amount  dissolved  from  the  precipi- 
tating boxes,  because  some  lead  is  always  coming  into  the 
system  in  the  slime  being  added,  but  it  is  evident  that  it  is 
necessary  to  have  a  certain  stock  on  hand  in  the  precipitating 
boxes,  if  all  or  nearly  all  of  the  antimony  and  arsenic  is  to  be 
precipitated.  What  escapes,  if  any,  has  still  to  be  electrolyzed 


374 


LEAD  REFINING  BY  ELECTROLYSIS. 


near  the  cathodes  of  the  electrolytic  tanks,  when  it  is  largely 
removed  in  the  cathode  lead. 

The  favorable  condition  of  the  cathode  lead  as  a  pre- 
cipitating material  was  due  to  the  solution  being  somewhat 
impure  in  respect  to  antimony  and  arsenic,  so  with  a  complete 
extraction  of  these  elements  in  the  precipitating  boxes,  it  would 
be  necessary  to  run  into  the  electrolytic  tank  a  little  solution 
still  containing  arsenic  and  antimony. 

The  ferric-iron  tank  produced  about  60  Ibs.  of  granular 
lead  daily,  which  was  removed  from  the  cathodes  every  12  or 
18  hours  and  shoveled  into  precipitating  boxes,  of  which  there 
were  eventually  four  in  series.  I  sampled  the  four  successive 
layers  of  one  box  which  had  been  taken  out,  with  the  results 
given  in  Table  131. 

TABLE  131. 


Layer. 

Lead. 

Copper. 

Antimony. 

Arsenic. 

Top 

none 

present 

47% 

25% 

No  2 

none 

42% 

45% 

No  3  . 

28% 

62% 

Bottom  .... 

13.2% 

40.5% 

Of  the  four  boxes  in  series,  and  while  they  were  still  operat- 
ing efficiently,  I  took  samples  as  follows :  Box  A  was  7x7  ins. 
and  contained  a  layer  about  4  ins.  deep.  Sample  AI  was  the 
top  quarter,  and  A2,  A3,  and  A4  the  following  quarters.  Box 
B  was  11x14  ins.  and  contained  a  layer  about  5J  ins.  deep. 
Samples  BI  to  B5  were  of  the  five  successive  inch  layers  from 
top  downwards.  C  was  a  pail  10 J  ins.  diameter  at  the  top 
and  8  ins.  diameter  at  the  bottom,  and  had  a  layer  about 
4  ins.  thick.  Samples  Ci  to  Cs  are  of  the  five  successive  layers 
from  the  top  down.  Box  D  was  11X9  ins.  and  contained  a 


APPENDIX. 


375 


layer  9J  ins.  deep.  Samples  DI  to  D4  are  from  the  four  layers 
of  equal  depth.  The  analyses  were  hurried  and  the  bismuth 
determinations  were  not  satisfactory.  In  a  general  way, 
samples  Ci  and  C2  contained  the  most  bismuth  and  a  good 
deal  of  it,  especially  Ci.  Cs  is  an  accurate  analysis  by  Mr. 
A.  E.  Knorr.  The  results  are  given  in  Table  132. 

TABLE  132. 


Number. 

Cu. 
Per  Cent. 

Bi, 
Per  Cent. 

Pb, 
Per  Cent. 

Sb, 
Per  Cent. 

As. 
Per  Cent. 

Of  Total 
Volume. 

A!  .  . 

40   2 

none 

trace 

35  7 

9  9 

2  3% 

t  

38.2 

none 

none 
trace 

41.8 
52  5 

12.3 
13.4 

2.3% 
2  3% 

1: 

24.3 
2  5 

trace 
none 

trace 
none 

51.0 
52  5  ? 

16.7 

2.3% 
8  0% 

B     ' 

64  5 

24  0 

B, 

none 

none 

none 

62  3 

25  1 

8  09^ 

B;.. 

none 

none 

68  2 

23  1 

8  0% 

B;  

Ct  

none 
0.75  / 

none 
33%  by 

none 
1     2.0 

57.5 
38  5 

25.7 

25  7 

8.0% 
2  4% 

C2  

Co.. 

1 
none  \ 
none 

difference 
13%  by 
difference 
10.9 

/ 
|  none 
2.5 

62.3 
59.5 

24.0 
23  2 

2.3% 
2  2% 

c 

trace 

2  2 

2  0 

43  9  ? 

14  6 

2  1% 

c 

none 

27? 

62  2 

19  9 

2  1% 

Dl. 

none 

trace 

13% 

56  6 

13  7 

9  9% 

D 

none 
none 

none 
none 

12 
13 

64  5 

13.6 
11   1  f 

9.9% 
9  9% 

D  ::::::: 

none 

none 

32.3 

61  7 

9  9% 

There  are  evidently  three  distinct  products,  the  first  of 
which  contains  nearly  all  the  copper,  and  would  probably 
contain  all  the  copper  with  a  better  arranged  set  of  'precipitat- 
ing tanks.  This  product,  I  believe,  would  be  nearly  pure 
copper  and  not  a  compound  of  copper  with  antimony  or  arsenic, 
as  copper  particles  had  been  already  formed,  and  it  is  probably 
only  a  question  of  time  until  the  antimony  and  arsenic  are 
all  dissolved  from-  the  upper  layers.  This  seems  all  the  more 
probable  since  antimony  and  arsenic  are  known  to  precipitate 


376  LEAD  REFINING  BY  ELECTROLYSIS. 

:  copper  itself  under  the  proper  conditions.  Further,  the  anti- 
.rnony  and  arsenic  are  in  an  ideal  condition  for  chemical  action 
.on  account  of  the  fine  division  of  the  particles  resulting  origi- 
;nally  from  their  precipitation  from  solution,  by  lead  particles. 
The  complete  absence  of  lead  from  this  product  and  the  follow- 
ing one  is  fortunate.  Whether  the  copper  product  essayed 
40%  or  more,  it  would  probably  go  to  a  copper  anode  furnace 
anyway. 

Bismuth  is  first  found  on  going  through  the  mass  from  the 
top  downward,  when  the  first  layers  containing  lead  are  reached, 
and  no  other  conclusion  is  possible,  except  that  the  bismuth  in 
the  solution  run  in  is  precipitated  by  lead  and  not  by  copper, 
antimony,  or  arsenic,  and  also  that  antimony  and  arsenic  are 
precipitated  by  bismuth  already  precipitated  itself  by  lead, 
while  the  bismuth  redissolves  and  passes  further  down  until 
it  comes  into  contact  with  metallic  lead  again.  The  bismuth 
must  pass  unprecipitated  through  the  copper  layers  and  the 
antimony-arsenic  layers  and  be  precipitated  in  the  first  lead. 
As  this  lead  dissolves  away  in  precipitating  arsenic  and  anti- 
mony, the  bismuth  must  dissolve  with  it  only  while  the  lead 
continues  hi  solution  and  flows  away,  the  bismuth  is  almost 
immediately  again  reprecipitated.  Given  a  mass  of  precipitating 
lead  into  which  the  slime  solution  flows,  the  longer  the  time 
allowed,  the  wider  will  be  the  respective  bands,  and  probably 
the  higher  will  be  the  percentage  of  copper  in  the  copper  product 
and  of  bismuth  in  the  bismuth  product.  Whether  the  bismuth 
layer  would  become  in  part  at  least  pure  bismuth  is  uncertain, 
but  it  makes  very  little  difference  as  we  have  a  simple  and 
practical  method  of  treatment.  This  is  by  stirring  the  product 
into  the  same  solution  as  is  used  for  treating  slime,  when  the 
bismuth,  being  now  more  concentrated  than  in  the  slime. 


APPENDIX.  377 

will  separate  for  the  most  part  as  insoluble  bismuth  fluoride, 
while  antimony,  arsenic,  and  lead  dissolve,  and  the  solution 
may  be  passed  through  the  precipitating  boxes  with  the  slime 
solution. 

The  principal  product,  in  quantity  at  least,  is  the  arsenic- 
antimony  layer.  This  is  fortunately  free  from  lead.  It  shows 
no  disposition  to  separate  into  two  layers,  one  of  antimony 
and  the  other  of  arsenic.  This  I  proved  by  taking  another 
sample,  several  days  later,  from  the  same  locality  that  sample 
J5i  was  taken.  It  contains  Sb  61%,  As  26.7%.  The  pro- 
portion of  the  two  metals  is  almost  exactly  the  same  as  the 
proportion  in  which  they  are  removed  from  the  slime. 

At  this  time  I  have  not  yet  had  the  opportunity  of  testing 
methods  of  recovering  the  antimony.  If  simply  heated  and 
melted  in  a  crucible  the  product  contains  17.2%  As,  and  by 
further  treating  in  a  carbon  crucible  nearly  to  a  white  heat 
the  arsenic  is  reduced  to  8.7%.  Exposing  the  melted  metal 
to  air  does  no  good.  37.5  grams  of  alloy  containing  8.7% 
arsenic  was  reduced  by  oxidation  to  31  grams,  but  arsenic 
was  still  as  high  as  7.6%.  Taking  account  of  the  vast  difference 
in  the  boiling-points  of  metallic  arsenic  and  antimony,  and  the 
absence  of  any  strong  combination  between  the  two,  sufficient 
heating  of  the  antimony  ought  to  give  a  complete  separation. 
Possibly  also  by  partial  oxidation  under  the  proper  furnace 
conditions  the  arsenic  can  be  got  off  as  As203  and  the  antimony 
left  as  metal.  I  expect  to  try  heating  the  metal  to  the  boiling- 
point  of  antimony  in  a  carbon  crucible  placed  in  an  electric 
furnace.  Arsenic  may  be  removed  by  treatment  with  sulphur. 

The  various  products  can  be  distinguished  by  their  appear- 
ance. The  copper  product  is  a  black  mud,  the  antimony- 
arsenic  product  is,  when  stirred  with  water  in  a  glass  vessel, 


378  LEAD  REFINING  BY  ELECTROLYSIS. 

flaky  like  mica,  and  brilliant,  while  the  bismuth  product  is 
intermediate  between  the  antimony-arsenic  product  and  the 
unchanged  lead. 

The  slime  treatment  itself  was  carried  out  in  barrels,  the 
method  being  to  stir  into  the  warm  anolyte,  containing  about 
2.5%  of  ferric  iron  as  it  came  from  the  electrolytic  plant,  a 
batch  of  slime  that  had  been  already  used  to  reduce  any  excess 
of  ferric  iron  left  in  the  solution  after  treatment  of  the  pre- 
vious batch.  The  slime  and  solution  were  stirred  generally 
for  about  half  an  hour,  using  with  our  weak  solution  about  2J 
cubic  feet  of  solution  for  a  6-lb.  lot  of  slime.  After  settling 
half  an  hour,  the  solution  was  decanted  to  another  barrel  with 
no  silver  or  merely  a  trace  in  solution,  and  in  one  case  when  a 
test  was  made  0.16  gram  of  solid  material  per  litre.  To  the 
decanted  solution  a  fresh  lot  of  slime  was  added  to  reduce  any 
ferric  iron.  In  this  way  each  lot  of  slime  and  each  lot  of  solu- 
tion was  treated  twice,  so  that  the  slime  was  thoroughly 
treated  and  the  solution  thoroughly  reduced  without  its  being 
required  to  get  the  exact  quantities  necessary  for  each  treat- 
ment. If  we  were  using  too  much  slime  the  titration  of  the 
solution,  after  being  put  on  slime  for  the  first  time,  would  rise 
with  each  batch,  when  the  size  of  the  slime  lots  could  be  di- 
minished. Some  45  lots  were  treated  altogether,  of  which  the 
first  were  removed  separately  while  the  last  one-half  or  so 
were  allowed  to  accumulate  in  the  slime-treating  barrel.  The 
various  lots  were  sampled  and  analyzed  for  silver  by  dissolving 
in  nitric  acid  and  titrating  with  NH4CNS  solution.  The 
results  by  this  method,  when  checked  up,  were  found  a  little 
low,  say  1  to  3%.  The  figures  are  given  in  Table  133. 


APPENDIX. 
TABLE  133. 


379 


Lot. 

Per  Cent 
Silver. 

Lot. 

Per  Cent 
Silver. 

Lot. 

Per  Cent 
Silver. 

5 

56   4 

17 

62   9 

28  1 

6 

54   7 

18 

67  1 

*w 

29  1 

7 

40  0 

19 

62  9 

•6E7      , 

30  f 

67.2 

9 

65  7 

20 

63  6 

31  1 

10  
11  

61.3 
61  9 

21 
22 

59.6 
57  3 

28] 
to  I 

67  4 

12  
13 

57.8 
53  4 

23 
24 

60.3 
56  2 

41  J 
42  1 

14 

61  6 

25 

61  8 

to  L 

15  and  16  . 

65  9 

26 

56  3 

54  | 

16  

63.1 

27 

61.8 

'^  J 

The  low  percentage  of  silver  in  some  few  lots  was  due  to 
the  use  of  too  much  slime  for  a  given  amount  of  solution.  An 
accurate  analysis  by  Mr.  A.  E.  Knorr  gave  for  the  original 
slime  the  figures  given  in  Table  134.  Our  figures  for  Lot  28 
to  41  by  his  method  and  the  percentages  of  extraction,  on  the 
assumption  that  the  weights  are  inversely  proportional  to  the 
percentages  of  silver,  are  also  given. 

TABLE  134. 


Raw  Slime. 

Treated  Slime. 

Percentage  of 
Extraction. 

Silver 

17  2% 

67  4% 

0  0 

Bismuth  . 

2  6%    * 

0  3% 

97  0 

Copper  

2.45%' 

0  2% 

97  9 

Lead  

11.9% 

7.8% 

83.1 

Antimony 

39  2% 

10  0% 

93  4 

Arsenic 

16  0% 

0  43% 

99  3 

Tellurium  

1  3% 

2  12% 

? 

Other  analyses  of  treated  slime  are  given  in  Table  135. 


380 


LEAD  REFINING  BY  ELECTROLYSIS. 
TABLE  135. 


Lot. 

Lead. 

Silver. 

Copper. 

Arsenic. 

Antimony. 

Bismuth. 

5  
6  

8.3% 

8.5% 

56.4% 

54.7% 

none 
none 

2-1% 
1.2% 

16.0% 
11.5% 

V.4% 
5.2% 

7 

15  6% 

40  0% 

none 

1  4% 

16  4% 

S  *2P7 

9 

5  2% 

65  7% 

none 

0  5% 

18  0% 

1  Q°7 

10  . 

7.4% 

61  3% 

none 

2.1% 

15  2% 

3  9% 

These  early  lots  are  not  as  representative  of  the  process 
as  the  later  combined  lots. 

Regarding  the  percentage  of  extraction  of  the  various 
metals  there  could  be  considerable  variation  even  if  there  was 
complete  oxidation  by  ferric  iron.  If  the  solution  contained 
too  much  hydrofluoric  acid  the  extraction  of  lead  would  be 
adversely  affected,  as  lead  fluoride  could  separate  in  the  slime. 
In  this  case  also  the  percentage  of  bismuth  extracted  would  be  a 
minimum.  On  the  other  hand  if  the  solution  contained  too 
little  HF  antimony  would  remain  in  the  slime  as  trioxide  in 
large  quantities.  In  this  case  bismuth  would  be  largely  or 
entirely  removed  as  fluosilicate.  My  results  indicate  that 
there  is  a  safe  mean  between  the  two  extremes.  A  ready 
method  of  control  is  to  dissolve  a  sample  of  the  treated  slime 
in  concentrated  H2S04,  dilute  to  500  c.c.,  add  50  cc.  HC1, 
and  titrate  with  permanganate  for  a  rough  antimony  titration. 
If  antimony  is  too  high  add  a  little  more  HF. 

From  the  standpoint  of  metal  recovery,  the  extractions 
were  pretty  satisfactory,  though  it  would  be  better  if  the 
silver  residue  was  left  in  a  purer  condition.  By  the  use  of 
stronger  and  warmer  solutions  there  would  be  an  improve- 
ment to  some  extent  at  least,  and  longer  agitation  of  slime 
with  solution  would  probably  help.  Theoretically  there  is 
no  reason  why  practically  all  the  base  metals  could  not  be 


APPENDIX.  381 

removed,  and  possibly  even  tellurium  could  be  removed  and 
recovered  by  a  certain  procedure. 

The  residue  from  the  slime  treatment  is  dense  and  solid 
and  occupies  a  very  small  fraction  of  the  space  occupied  by 
the  raw  slime  itself.  It  filters  rather  slowly  in  the  cold,  but 
washes  rapidly  with  hot  water. 

Arsenic  fumes  were  noted  for  a  few  hours  during  the  first 
run,  but  no  arsenic  was  evolved  from  the  solution  or  apparatus 
after  the  copper,  antimony,  and  lead-arsenic  depositing  tanks 
were  cut  out. 

For  a  commercial  plant  the  following  points  are  worth 
considering. 

The  electrolytic  tanks  for  depositing  lead  and  producing 
ferric  iron  could  use  diaphragms  of  cotton  duck  stretched  on 
wooden  frames.  The  frames  should  surround  the  cathodes 
and  not  the  anodes,  as  in  my  apparatus,  because  when  renewals 
are  required,  which  would  probably  be  about  once  a  month, 
the  cathodes  are  more  easily  removed  than  the  anodes.  The 
frames  or  boxes  would  be  pulled  out,  new  duck  stretched  on 
and  replaced.  These  boxes  should  be  open  at  the  bottom,  and 
not  quite  reach  the  bottom  of  the  tank.  The  heavy  anolyte 
lying  in  the  bottom  of  the  tanks  would  dissolve  any  soft  lead 
falling  from  the  cathodes  and  prevent  a  troublesome  accumu- 
lation, without  affecting  the  cathodes,  provided  they  did  not 
reach  too  low  in  the  tank.  The  anolyte  with  this  construction 
could  be  readily  circulated  throughout  the  tank,  a  very  de- 
sirable thing.  The  cathodes  should  best  be  of  copper  sheet 
and  the  tanks  should  be  served  by  a  crane  so  that  the  cathodes 
could  be  lifted  out  and  away  every  twelve  hours  and  the  lead 
wiped  off  by  the  tank  load,  an  operation  that  would  take  but 
a  few  minutes  with  apparatus  like  that  shown  on  page  245. 


382  LEAD  REFINING  BY  ELECTROLYSIS. 

The  feed  of  solution  would  be  divided  as  equally  as  possible 
between  the  cathode  compartments,  while  the  discharge  would 
be  merely  through  an  overflow  hose.  A  current  density  of 
10  amperes  would  probably  be  near  the  upper  limit  if  it  was 
desired  to  oxidize  most  of  the  ferrous  iron.  The  voltage  would 
be  about  two  volts. 

The  slime  treatment  probably  need  not  be  conducted  in 
separate  batches  of  regulated  size.  A  whole  day's  production 
of  slime  could  probably  be  placed  in  one  tank,  and  anolyte 
from  the  tank  allowed  to  collect  there  tor  perhaps  an 
hour,  when  it  could  be  stirred  and  settled  and  the  solution 
passed  to  the  precipitating  boxes.  In  this  way  the  lead  and 
bismuth  might  be  removed  first  and  the  copper  last,  but  as 
the  precipitation  of  the  metals  is  automatic  there  is  no  neces- 
sity for  a  constant  composition  of  solution  passing  through  the 
precipitators. 

The  precipitation  boxes  should  all  have  downward  per- 
colation because  the  outflowing  solution,  containing  more 
lead,  is  heavier  than  the  inflowing.  A  little  consideration  shows 
that  the  metals  should  stratify  horizontally  under  these  con- 
ditions. By  skilful  regulation  it  is  probable  that  the  different 
products  could  be  collected  in  separate  boxes  if  desired.  If 
not  the  different  layers  could  be  detected  by  the  different 
appearance.  The  washing  ought  to  be  easy,  if  water  is  added 
at  the  top  to  displace  the  heavier  solution,  for  the  material  is 
of  a  very  open,  pervious  nature.  The  material  in  the  boxes 
would  be  kept  flooded  at  all  times  except  when  unloading 
by  having  the  discharge  at  a  level  about  the  same  as  that  of 
the  top  of  the  material.  The  resistance  of  the  metal  to  the 
flow  of  the  solution  is  very  slight  and  is  hardly  to  be  con- 
sidered. 


APPENDIX.  383 

The  solution  flowed  through  one  of  the  boxes  in  my  experi- 
ment at  the  rate  of  40  inches  per  hour,  which  was  far  too  high. 
A  speed  of  4  inches  per  hour  would  not  make  the  size  of  the 
precipitating  tanks  inconveniently  large  at  all,  and  would  give 
a  better  chance  for  the  reactions  to  occur  at  the  proper  place, 
and  would  not  allow  the  different  metals  to  get  beyond  their 
respective  zones  of  precipitation. 

The  control  of  the  process  would  be  by  titrating  samples 
of  the  solution  flowing  from  the  electrolytic  tanks  by  standard 
permanganate  solution.  The  action  on  the  slime  can  be  followed 
in  the  same  way. 

For  following  the  operation  of  the  precipitating  tanks, 
titrating  the  inflowing  and  outflowing  solution  by  permanga- 
nate, or  taking  the  specific  gravity  of  each,  should  give  the 
desired  information.  In  these  titrations  the  permanganate 
oxidizes  antimony  and  iron  both,  and  will  certainly  oxidize 
arsenic  in  presence  of  HC1,  and  probably  in  presence  of  H2S04. 

If  the  slime-treating  solution  accumulates  lead  fluosilicate, 
on  account  of  the  use  of  slime  not  thoroughly  washed,  an 
electrolytic  method  exists  for  taking  this  out  again  in  the  form 
of  pure  lead  fluosilicate. 


INDEX. 

Acid  fluosilicic,  30 

fluosilicic  preparation,  174,  305 

hydrofluoric  preparation,  174 

loss  in  evaporation,  323 

loss  in  refining  lead,  32,  33,  35,  41,  42,  185,  253,  329 

loss  in  slime,  35,  270,  367 

loss  on  anode  scrap,  270 

loss  on  cathodes,  38,  40,  269 

on  surfaces,  37 
Alloys  in  anodes,  6,  54,  55 
Analyses,  anode  slime,  13,  57,  61,  99,  100,  116,  121,  133,  288,  289,  358,  369 

anode  slime,  treated,  379,  380 

dore  bullion,  113,  160 

dore  bullion  from  copper  slime,  101 

dross  from  melting  cathodes,  198,  202 

electrolytic  antimony,  60 

material  precipitated  from  slime  solution,  374,  375 

refined  lead,  13,  57,  284,  290,  298 
Analysis,  methods  of,  295 
Anode  molds,  199,  202,  203,  316,  317 

molds,  closed,  209,  317 
Anodes,  casting,  203 

insoluble,  of  carbon,  361 

insoluble,  of  lead,  for  antimony-depositing,  144,  259 

scrap  from,  255,  316 

storage  of,  251 

sulphur  in,  46 

tin  in,  46,  47 

weight  of,  316 
Anode  slime,  amalgamation  of,  62 

amount  of  lead  in,  53,  54 

bismuth  in,  54,  76 

chlorination  of,  68,  69,  71 

chlorination  of  alloys  from,  67,  68 

drying,  256,  346 

385 


386  LEAD  REFINING  BY  ELECTROLYSIS. 

Anode  slime,  extraction  of  metals  from,  76,  79,  98,  100,  112,  113,  118,  130, 
134,  135,  137,  323,  356,  367,  379,  380 

from  copper  refining,  95,  100,  101 

fusion  of,  71-73 

fusion  of,  products,  76,  77 

fusion  of  slags,  72 

fusion  to  alloy,  63-65 

iron-reducing  power  of,  358 

melting,  see  also  Anode  slime  fusion,  63-65,  71-79,  256,  257,  325 

melting  with  sulphur,  78,  79 

metals  in,  46 

oxidation  of,  96,  126,  128,  358 

physical  condition  of,  181 

polarized  condition  of,  49,  53 

porosity  of,  48 

roasting,  128 

roasting  with  H2SO4,  129 

silica  in,  35,  36 

treatment  with   combined  fluosilicate  and  fluoride  solution,    120,  121, 
125,  134,  355 

treatment  with  combined  sulphate  and  fluoride  solution,  116,  117 

treatment  with  copper  fluosilicate,  125 

treatment  with  ferric  fluosilicate,  355 

treatment  with  ferric  salts  of  monobasic  acids,  119 

treatment  with  fluosilicate  solutions,  91 

treatment  with  sodium  sulphide,  100,  123,  124,  323 

used  as  anode,  83,  85,  88,  126 

washing,  249,  271,  321,  322,  346 
Antimony,  as  precipitant  for  copper,  144,  145,  370,  371 

electrolytic  refining  of,  138 

extraction  by  ferric-fluosilicate+HF  process,  379 

extraction  by  ferric-sulphate  process,  112 

extraction  by  HF,  97 

fluoride  electrolyte,  88,  138,  139 

in  anode  slime,  54,  56 

in  melting  slag,  volatilization  of,  74 

precipitation  by  lead,  371,  377,  382 
Antimony-depositing,  anodes  for,  see  Anodes  insoluble. 

cathodes  for,  259 

efficiency,  143,  324 

from  fluoride  solution,  135,  143 

from  sulphide  solution,  323 

tanks  for,  259 

with  soluble  lead  anodes,  360,  363,  367,  370,  379 
Arsenic  in  anode  slime,  52 

in  deposited  antimony,  146 


INDEX.  387 


Arsenic  in  sulphate  solutions,  102 
lead  alloy,  deposition  of,  364 
precipitation  by  lead,  371-377,  382 

Arsenious  acid  in  sulphate  solutions,  102 

Ashcroft,  E.  A.,  8,  70 

Balbach,  E.,  155,  156,  158 

Benzenesulphonic  acid,  see  Lead  benzenesulphonate. 

Bibliography,  309 

Bismuth  chloride  electrolyte,  89 
in  anode  slime,  54,  76 
methyl  sulphate  electroylte,  89 
precipitation  by  lead,  375,  376 
solubility  in  fluoride  solutions,  112 
solubility  in  sulphate  solutions,  115 
recovery  by  ferric  fluosilicate  +  HF  process,  375 
recovery  from  sulphate  solutions,  115 

Body,  102 

Borchers,  W.,  8,  124,  309 

Brewer,  A.  K.,  160 

Bus-bars,  315,  345 

By-products  from  smelting,  291 

Cadmium-fluosilicate  solution,  18 
Carhart,  Willard  and  Henderson,  167 
Cascade  system  of  tanks,  223,  241 
Casting  anodes,  203,  212 

anodes  in  closed  molds,  209 

cathodes,  230,  314,  319,  344 

lead  from  cathodes,  320,  346 
Catalysis  of  methyl  acetate  test,  19 
Cathode  deposit,  weight  of  per  square  foot,  40,  184 
Cathodes,  casting,  230,  319,  344 

cleaning,  268-269 

for  antimony-depositing,  259,  328 

for  lead-depositing,  228,  229 

hanging,  319 

loss  of  acid  on,  38,  40,  269 

melting,  320 

of  deposited  lead,  229 

placing  in  tanks,  319 

steel  for  lead  depositing,  229,  267 

supporting  bars  for,  231,  233 
Chlorides,  reduction  by  lead,  70 
Chlorination  of  alloys  from  slime,  67,  78 

of  dry  slime,  68,  69 


388  LEAD  REFINING  BY  ELECTROLYSIS. 

Chlorination  of  wet  slime,  71 

Chlorine  storage,  70 

Cia   Minera  Fundidora  y  Afinadora,  Monterey,  Mex.,  160 

Circulation  of  anolyte  and  catholyte  ferric-iron  tanks,  263 

of  lead-depositing  solution,  211,  237,  239,  344 
Cleaning  anodes  and  cathodes,  268,  269 

tanks,  234,  268,  321 

Composition  of  lead-refining  electrolyte,  41,  43,  187,  328,  346 
Condensers  for  hydrofluoric  acid,  176 
Conductivity  of  various  solutions,  17,  28 

determinations,  306 
Consolidated  Mining  and  Smelting  Co.  of  Canada,  plant  at  Trail,  B.  C.,  255, 

284,  312 

Contamination  of  cathodes  by  slime,  235,  285 
Contacts,  237,  315 
Copper  addition  to  alloy  from  slime,  90 

anode  slime,  95,  100,  101 

deposition  of  from  slime  solution,  131 

deposition  with  antimony  anode,  360,  363,  367,  370 

fluoride  electrolyte,  90 

in  anode  slime,  53 

lead  alloy,  treatment  of,  291 

matte,  95 

matte  leaching,  114 

matte  roasting,  114 

precipitation  by  antimony,  144,  145,  370,  371 

process  of  Siemens  and  Halske,  93,  102 

scale,  114 
Cost  of  concrete  tank,  219 

of  depositing  antimony,  148 

of  glue  or  gelatine,  183 

of  labor  in  tank-room,  272,  273 

of  lead-depositing  electrolyte,  242 

of  lead-refining  plant,  190,  191,  277,  283 

of  making  cathodes,  271,  319 

of  making  hydrofluoric  acid,  177 

of  melting  lead,  273 

of  molding  anodes,  316 

of  power  influenced  by  current  density,  187,  188 

of  power  influenced  by  solution  composition,  188,  189 

of  power  lost  in  bus-bars,  227 

of  refining  lead,  272,  273 

of  refining  lead,  comparative,  274-276,  279 

of  steel  cathodes,  229 

of  treating  slime,  191-196 

of  unloading  lead,  345 


INDEX.  389 


Cranes,  250,  313,  344 

Current  density,  consideration  of,  183-191 

density,  limiting,  53 

efficiency,  lead-depositing,  209,  329 

Decomposition  of  fluosilicic  acid  by  lead  bases,  30,  246 

of  fluosilicic  acid  by  electrolysis,  33,  34 
Depreciation  of  tanks,  185 

Determination  of  conductivity  of  solutions,  306 
Diaphragms,  109,  110,  152,  262,  264,  265 

of  carbon,  357,  360,  368 

of  cotton,  368,  381 
Dietzel,  Dr.,  150-152 
Distillation  of  anode  slime,  60,  62,  63 
Distribution  of  metals,  extracting  with  H2SiF6+HF,  137 

ferric-sulphate  process,  97,  98 

ferric-sulphate  and  HF  process,  137 

melting  slime,  76,  79 

roasting  with  H2SO4  process,  133 
Dithionic  acid,  see  Lead  dithionate. 
Dore"  bullion  refining,  149 

in  furnace,  149,  150 
Drawing  cathodes,  201,  285,  320 
Dross  from  melting  cathodes,  198 
Drying  slime,  256,  325,  346 

Easterbrooks,  F.  D.,  155 

Efficiency  of  electric  current  affected  by  gelatine,  16 

of  electric  current  in  antimony  deposition,  324 

of  electric  current  in  lead  deposition,  329 
Electric  furnace,  74,  75 

Electrolysis  for  ferric-sulphate  solution,  101-109 
Electrolyte,  introducing  lead  into,  243 
Electrolytic  conductivity,  19 

refining  rule  of,  4 
Electromotive  forces  of  solution  of  metals,  450-452 

forces  of  solution  of  alloys,  6 
Ethyl  sulphuric  acid,  see  Lead  ethyl  sulphate. 
Eurich,  E.  FM  274 
Evaporation,  acid  loss  in,  see  Acid  loss. 

lead-depositing  electrolyte,  252,  323 

of  fluosilicic  acid,  29 

of  water  from  electrolyte,  254 
Experimental  tanks,  305 
Extraction  of  metals  from  slime,  see  Anode  slime. 


390  LEAD  REFINING  BY  ELECTROLYSIS. 

Factors  for  calculating  ferric  iron,  96 

influencing  amount  of  lead  in  slime,  53 
Faraday's  law,  3 
Ferric  chloride  for  treating  slime,  92 

fluosilicate  for  treating  slime,  348 

sulphate,  action  of,  94 

sulphate  for  treating  slime,  93,  94 
Ferrous  sulphate,  oxidation  by  air,  127 
Filtration  of  sulphate  slime  solution,  97 

of  slime,  322,  346 

Fluoboric  acid,  see  Lead  fluoborate. 
Fluoride  of  antimony,  etc.,  see  Antimony  fluoride,  etc, 
Fluosilicic  acid  in  hydrofluoric  acid,  140,  147 

preparation,  178,  305 

see  also  Lead  fluosilicate. 
Fluxes  for  melting  to  dore,  113 
Floors  under  tanks,  236 
Foundations  for  tanks,  233,  344 
Free  HF  in  lead-refining  solution,  30,  32,  ?6 

Gelatine,  14,  15,  22,  130,  158,  159,  170,  183 

quantity  required,  42 

in  silver-depositing  electrolyte,  170 
Glue,  see  Gelatine. 

Haber,  F.,  309. . 
Hanging  cathodes,  319 
Hydrofluoric  acid  manufacture,  174 

yield,  243 

Hofman,  H.  O.,  310 
Hofmann,  O.,  258 

Hook  for  lifting  cathodes,  Plate  II,  337 
Howard  skimmer,  198 

Inspecting  tanks,  270,  326 

Interest  charges- on  lead,  183,  184,  276 

on  silver  and  gold,  156,  157,  160,  170 
Inversion  of  cane-sugar  test,  19 
Iron  cathodes,  12 

in  anodes,  46 

see  also  Cathodes,  steel. 

Jacobs,  E.,  319 

Keith,  N.  S.,  10 
Keith  process,  10,  309 


INDEX.  391 

Kern,  E.  F.,  27,  50,  54,  291,  293,  310,  311 

Labor  for  loading  and  unloading  lead,  272,  327 

for  making  cathodes,  271,  319 

for  melting  lead,  273,  320,  327 

for  tank-room,  272,  326 

for  treating  slime,  328 
Leaching  apparatus,  257 
Lead  acetate,  refining  solution,  10,  11 

alkaline  solutions  of,  11 

benzenesulphonate  solution,  17,  19,  20-22 

chloride  electrolyte,  7,  65.  69 

deposits,  smoothness  of,  16 

deposits,  specific  gravity  of,  13 

dithionate  preparation,  26 

dithionate  solution,  17,  20,  22,  25 

ethylsulphate  solution,  17,  19,  23 

fluoborate  solution,  17,  20-22,  28 

fluoride,  8 

fluosilicate,  conductivity,  28,  43,  <*5 

fiuosilicate,  crystallization,  31 

fluosilicate,  preparation,  30 

fluosilicate  solution,  17,  20-22,  32 

hydroxide  theory,  12 

melting,  see  Melting. 

oxychloride  and  chloride  bath,  8 

peroxide,  27,  58,  92,  93,  119-122,  154 

phenolsulphonate  solution,  23,  24 

preparation  of  pure,  58,  59 

siphon,  197 

sulphide  and  chloride,  7 
Ledoux  and  Co.,  301 
Levels  in  refinery,  197 
Limiting  current  density,  53 

Locke,  Blackett  and  Co.,  Ltd.,  plant  at  Newcastle-on-Tyne,  183 
Losses  at  contacts,  see  Contact  loss. 
Loss  of  acid,  see  Acid  loss. 

Mattes  of  silver  and  copper,  treatment  of,  78 

from  anode  slime,  76-78,  79 
McNab,  Alexander,  323 
Mechanical  casting  of  lead,  202 
Melting  lead,  198,  201,  202,  345,  320 

see  also  Anode  slime. 

slime,  325 
Mennicke,  H.,  18,  309 


392  LEAD  REFINING  BY  ELECTROLYSIS. 

Metals  in  slime,  46 

in  solution,  46 
Method  of  analysis  of: 

antimony,  297 

antimony  fluoride  electrolyte,  304 

dore"  bullion,  297 

electrolyte,  302 

hydrofluoric  acid,  177 

matte  from  melting  slime,  303 

refined  lead,  298 

silica  in  slime,  304 

slags  from  melting  slime,  302 

slime,  295 

Methyl  sulphuric  acid,  preparation  of,  168,  169 
Miller,  J.  F.,  231,  311,  314 
Moebius,  B.,  155,  157,  158 
Molds  for  anodes,  202,  203,  316,  317 
Moving  insoluble  anodes,  103.  261 
Multiple  system,  180-182 

Nebel,  Moebius  and,  process,  159-164 

Operation  of  refinery,  167 

Ostwald,  W.,  quoted,  18 

Oxidation  of  antimony  at  insoluble  anodes,  135,  141,  142 

of  electrolyte  by  air,  96,  239,  241,  243 

of  ferrous  sulphate  by  air,  127 

of  slime  by  air,  126-129,  134,  256 

Patents,  309 

Philadelphia  mint,  silver  refining,  159 
Platinum  in  anode  slime,  54 
Polarization  in  lead  refining,  189 

of  anode  slime,  49 

with  insoluble  anodes,  364 
Porosity  of  anode  slime,  48 
Power  cost,  see  Cost. 
Precipitation  of  fluosilicates,  141 
Pumps  for  lead,  316,  320 

for  refinery  solution,  239 
Purification  of  lead-refinery  solution,  58 
Pyrogallol,  14,  15 

Refining  dore",  see  Dore". 

antimony,  see  Antimony. 


INDEX.  393 


Resorcin,  14 

Revolving  cathode,  11,  19 

for  fused  bath,  9 
Rich  lead,  refining,  99 
Roasting  slime,  128,  129 

copper  matte,  114 
Rosing  lead  pump,  197 
Rome,  N.  Y.,  plant  at,  10 
Ryan,  F.  C.,  246 

Saligenin,  14 

Sampling  lead  bullion,  213 

dore  bullion,  298 

Scrap  from  anodes,  180,  244,  246,  255,  316 
Selby  Smelting  and  Lead  Company,  298 
Selenium,  94 

Senn,  H.,  17,  34,  36,  54,  294,  309 
Series  system,  180,  182,  281-283 
Sherry,  R.  H.,  8,  20 

Siemens  and  Halske  copper  process,  93,  102 
Silica  in  solution  and  slime,  32-36,  57,  98 

deposit  on  carbon  anodes,  109 

use  in  slime  fusion,  135,  257 
Silver  amyl  sulphate  solution,  166 

deposition  of  solid,  165-167 

dissolved  in  roasting  with  sulphuric  acid  process,  130,  135 

distillation  of,  63 

methyl  sulphate  solution,  152,  166 

perchlorate  electrolyte,  167 

precipitation  from  ferric  sulphate  solution,  99 

sulphide  converted  to  metallic,  78 
Slag  from  melting  slime,  72,  76,  79 

reduction,  66,  82,  83 

treatment  of,  80-83 
Slime,  see  Anode  slime. 
Snowdon,  R.,  15 
Soda,  use  in  slime  melting,  71 
Sodium  sulphide  for  treating  slime,  100,  124,  323 
Specific  gravity  of  lead  deposits,  13,  16,  22 
Storage  of  anodes,  251 

of  solution,  241 
Strength  of  acids,  18-21 
Sulphur  in  anodes,  46 

Tank  systems,  180,  182,  227,  228,  241,  313,  343 
Tanks  for  antimony-depositing,  259 


394  LEAD  REFINING  BY  ELECTROLYSIS. 

Tanks  for  lead-depositing,  213,  214 

for  lead-depositing,  size  of,  214 

for  lead-depositing  of  concrete,  215,  234,  235 

for  lead-depositing  of  wood,  220 

for  lead-depositing  of  wood,  corrosion  of  bolts,  220,  224 

for  making  ferric  sulphate,  260,  266,  306 

for  slime  treatment,  323 
Tellurium,  94 

Temperature  of  refining  solutions,  44,  187 
Thum,  F.  A.,  223 
Thum,  Wm.,  155,  171 
Tin  fluosilicate  solution,  18 

fluosilicate  solution  for  refining,  47 

in  anodes,  46-48 
Tommasi,  D.,  11 
Tray  for  catching  drips,  319,  320 
Truswell,  R.,  209,  311 

United  States  Metal  Refining  Co.'s  plant,  202,  255,  331 
Ulke,  T,  310 

Valentine,  W.,  140,  231,  271 

Watt  and  .Phillip,  quoted,  10 
Washing  cathodes,  39 

electrodes,  244,  345 

slime,  246,  271,  321,  322,  346 
Whitehead,  R.  L.,  309 

Zinc  chloride  in  fused-lead  chloride,  8 


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Bernadou's  Smokeless  Powder,  Nitro-cellulose.  and  the  Theory  of  the  Cellulose 

Molecule i2mo,  2  50 

Chase's  Art  of  Pattern  Making i2ino,  2  50 

Screw  Propellers  and  Marine  Propulsion 8vo,  3  oo 

Cloke's  Gunner's  Examiner 8vo,  i  50 

Craig's  Azimuth 4to,  3  50 

Crehore  and  Squier's  Polarizing  Photo-chronograph 8vo,  3  oo 

*  Davis's  Elements  of  Law 8vo,  2  50 

*  Treatise  on  the  Military  Law  of  United  States 8vo,  7  oo 

Sheep,  7  50 

De  Brack's  Cavalry  Outpost  Duties.     (Carr.) 24010,  mor.  2  oo 

*  Dudley's  Military  Law  and  the  Procedure  of  Courts-martial. .  .  Large  i2mo,  2  50 
Durand's  Resistance  and  Propulsion  of  Ships 8vo,  5  oo 

2 


*  Dyer's  Handbook  of  Light  Artillery izmo,  3  oo 

Eissler's  Modern  High  Explosives 8vo,  4  oo 

*  Fiebeger's  Text-book  on  Field  Fortification Large  i2mo,  2  oo 

Hamilton  and  Bond's  The  Gunner's  Catechism i8mo,  i  oo 

*  Hoff's  Elementary  Naval  Tactics 8vo,  i  50 

Ingalls's  Handbook  of  Problems  in  Direct  Fire 8vo,  4  oo 

*  Lissak's  Ordnance  and  Gunnery 8vo,  6  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables 8vo,  i  oo 

*  Lyons's  Treatise  on  Electromagnetic  Phenomena.  Vols.  I.  and  II.  .8vo,  each,  6  oo 

*  Mahan's  Permanent  Fortifications.     (Mercur.) .  .  .  ; 8vo,  half  mor.  7  50 

Manual  for  Courts-martial i6mo,  mor.  i  50 

*  Mercur's  Attack  of  Fortified  Places I2mo,  2  oo 

*  Elements  of  the  Art  of  War 8vo,  4  oo 

Metcalf's  Cost  of  Manufactures — And  the  Administration  of  Workshops.  .8vo,  5  oo 

*  Ordnance  and  Gunnery.     2  vols Text  i2mo,  Plates  atlas  form  5  oo 

Nixon's  Adjutants'  Manual 24010,  i  oo 

Peabody's  Naval  Architecture 8vo,  7  50 

*  Phelps's  Practical  Marine  Surveying 8vo,  2  50 

Powell's  Army  Officer's  Examiner I2mo,  4  oo 

Sharpe's  Art  of  Subsisting  Armies  in  War i8mo,  mor.  i  50 

*  Tupes  and  Poole's  Manual  of  Bayonet  Exercises  and    Musketry  Fencing. 

24mo,  leather,  50 

*  Weaver's  Military  Explosives 8vo,  3  oo 

Woodhull's  Notes  on  Military  Hygiene i6mo,  I  50 


ASSAYING. 

Betts's  Lead  Refining  by  Electrolysis 8vo,  4  oo 

Fletcher's  Practical  Instructions  in  Quantitative  Assaying  with  the  Blowpipe. 

i6mo,  mor.  i  59 

Furman's  Manual  of  Practical  Assaying ; 8vo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments.  .  .  .8vo,  3  do 

Low's  Technical  Methods  of  Ore  Analysis 8vo,  3  oo 

Miller's  Cyanide  Process I2mo,  i  oo 

Manual  of  Assaying i2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) i2mo,  2  50 

O'DriscolI's  Notes  on  the  Treatment  of  Gold  Ores 8vo,  2  oo 

Ricketts  and  Miller's  Notes  on  Assaying 8vo,  3  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) .' 8vo,  4  oo 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 

Wilson's  Chlorination  Process i2mo,  i  50 

Cyanide  Processes i2mo,  i  50 


ASTRONOMY. 

Comstock's  Field  Astronomy  for  Engineers 8vo,  2  50 

Craig's  Azimuth 4*0,  3  50 

Crandall's  Text-book  on  Geodesy  and  Least  Squares 8vo,  3  oo 

Doolittle's  Treatise  on  Practical  Astronomy 8vo,  4  oo 

Gore's  Elements  of  Geodesy 8vo,  2  50 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  2  50 

*  Michie  and  Harlow's  Practical  Astronomy 8vo,  3  oo 

Rust's  Ex-meridian  Altitude,  Azimuth  and  Star-Finding  Tables.     (In  Press.) 

*  White's  Elements  of  Theoretical  and  Descriptive  Astronomy i2mo,  2  oo 

3 


CHEMISTRY. 

Abderhalden's  Physiological  Chemistry  in  Thirty  Lectures.     (Fall  and  Defren). 
(In  Press.) 

*  Abegg's  Theory  of  Electrolytic  Dissociation,    (von  Ende.) i2mo,  i   25 

Adriance's  Laboratory  Calculations  and  Specific  Gravity  Tables i2mo,  i  25 

Alexeyeff's  General  Principles  of  Organic  Syntheses.     (Matthews.) 8vo,  3  oo 

Allen's  Tables  for  Iron  Analysis 8vo,  3  oo 

Arnold's  Compendium  of  Chemistry.     (Mandel.) Large  i2mo,  3  50 

Association    of  State  and  National  Food  and  Dairy  Departments,  Hartford 

Meeting,  1906 Svo,  3  oo 

Jamestown  Meeting.  1907 Svo,  3  oo 

Austen's  Notes  for  Chemical  Students I2mo,  I  50 

Baskerville's  Chemical  Elements.     (In  Preparation). 

Bernadou's  Smokeless  Powder.—  Nitro-cellulose,  and  Theory  of  the  Cellulose 

Molecule 121110,  2  50 

*  Blanchard's  Synthetic  Inorganx  Chemistry i2mo,  i  oo 

*  Browning's  Introduction  to  the  Rarer  Elements Svo,  i  50 

Brush  and  Penfield's  Manual  of  Determinative  Mineralogy Svo,  4  oo 

*  Claassen's  Beet-sugar  Manufacture.     (Hall  and  Rolfe.) Svo,  3  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.    (Boltwood.).  .Svo,  3  oo 

Cohn's  Indicators  and  Test-papers I2mo,  2  oo 

Tests  and  Reagents Svo,  3  oo 

*  Danneel's  Electrochemistry.      (Merriam.) i2mo,  i   25 

Duhem's  Thermodynamics  and  Chemistry.     (Burgess.) Svo,  4  oo 

Eakle's  Mineral  Tables  for  the  Determination  of  Minerals  by  their  Physical 

Properties Svo,  125 

Eissler's  Modern  High  Explosives Svo,  4  oo 

Effront's  Enzymes  and  their  Applications.     (Prescott.) Svo,  3  oo 

Erdmann's  Introduction  to  Chemical  Preparations.     (Dunlap.) I2mo,  i   25 

*  Fischer's  Physiology  of  Alimentation Large  I2mo,  2  oo 

Fletcher's  Practical  Instructions  in  Quantitative  Assaying  with  the  Blowpipe. 

i2mo,  mor.  i  50 

Fowler's  Sewage  Works  Analyses i2mo,  2  oo 

Fresenius's  Manual  of  Qualitative  Chemical  Analysis.     (Wells.) Svo,  5  oo 

Manual  of  Qualitative  Chemical  Analysis.  Part  I.  Descriptive.  (Wells.)  Svo,  3  oo 

Quantitative  Chemical  Analysis.     (Cohn.)     2  vols 8vo;  12  50 

When  Sold  Separately,  Vol.  I,  $6.     Vol.  II,  S8. 

Fuertes's  Water  and  Public  Health i2mos  i  50 

Furman's  Manual  of  Practical  Assaying 8vo;  3  oo 

*  Getman's  Exercises  in  Physical  Chemistry i2mo  2  oo 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo  i  25 

*  Gooch  and  Browning's  Outlines  of  Qualitative   Chemical  Analysis. 

Large  121110,  i   25 

Grotenfelt's  Principles  of  Modern  Dairy  Practice.     (Woll.) i2mo,  2  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  i  25 

Hammarsten's  Text-book  of  Physiological  Chemistry.     (Mandel.) Svo,  4  oo 

Hanausek's  Microscopy  of  Technical  Products.     (Win ton.) Svo,  5  oo 

*  Haskins  and  Macleod's  Organic  Chemistry i2mo,  2  oo 

Helm's  Principles  of  Mathematical  Chemistry.     (Morgan.) I2mo,  i  50 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.  2  50 

*  Herrick's  Denatured  or  Industrial  Alcohol Svo.  4  oo 

Hinds's  Inorganic  Chemistry 8vo,  3  oo 

*  Laboratory  Manual  for  Students i2mo,  i  oo 

*  Holleman's    Laboratory   Manual    of   Organic    Chemistry  for   Beginners. 

(Walker.) i2mo,  i  oo 

Text-book  of  Inorganic  Chemistry.     (Cooper.) Svo,  2  50 

Text-book  of  Organic  Chemistry.     (Walker  and  Mort.) Svo,  2  50 

Holley  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments,  and  Varnishes. 

Large  121110  2  50 

4 


Hopkins's  Oil-chemists'  Handbook , 8vo,  3  oo 

Iddings's  Rock  Minerals 8vo,  5  oo 

Jackson's  Directions  for  Laboratory  Work  in.  Physiological  Chemistry.  .8vo,  i  25 

Joiiannsen's  Determination  of  Rock -forming  Minerals  in  Tliin  Sections..  .8vo,  4  oo 

Keep's  Cast  Iron 8vo,  2  50 

Ladd's  Manual  of  Quantitative  Chemical  Analysis xarno,  i  oo 

1/andauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

*  i>.ing\vorthy  and   Austen's   Occurrence   of  Aluminium  in  Vegetable  Prod- 

ucts, Animal  Products,  and  Natural  Waters Svo,  2  oo 

Lassar-Cohn's  Application  of  Some  General  Reactions  to  Investigations  in 

Organic  Chemistry.  (Tingle.) i2mo,  i  oo 

Leach's  Inspection  and  Analysis  of  Food  with  Special  Reference  to  State 

Control 8vo,  7  50* 

Lob's  Electrochemistry  of  Organic  Compounds.  (Lorenz.) Svo,  3  oo 

Lodge's  Notes  on  Assaying  and  Metallurgical  Laboratory  Experiments.  ..  .8vo,  3  oo 

Low's  Technical  Method  of  Ore  Analysis.  '.'. 8vo,  3  oo 

Lunge's  Techno-chemical  Analysis.  (Cohn.) , I2mo  i  op 

*  McKay  and  Larsen's  Principles  and  Practice  of  Butter- making Svo,  i  50 

Maire's  Modern  Pigments  and  their  Vehicles i2mo,  2  oo 

Mandel's  Handbook  for  Bio-chemical  Laboratory i2mo,  i  50 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe.  .  i2mo,         60 
Mason's  Examination  of  Water.     (Chemical  and  Bacteriological.).  .  ..i2mo,  i   25 

Water-supply.     (Considered  Principally  from   a    Sanitary   Standpoint.) 

Sva,.  4  oo 

Matthews's  The  Textile  Fibres.    2d  Edition,  Rewritten .8vo,  4  oo 

Meyer's  Determination  of  Radicles  in  Carbon  Compounds.     (Tingle.).  .I2mo,  i  oo 

Miller's  Cyanide  Process '. i2mo,  i  oo 

Manual  of  Assaying r2mo,  i  oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.) i2mo,  2  50 

Mixter's  Elementary  Text-book  of  Chemistry I2mo,  i  50' 

Morgan's  Elements  of  Physical  Chemistry I2mo,  3  co; 

Outline  of  the  Theory  of  Solutions  and  its  Results i2mo,  i  oo 

*  Physical  Chemistry  for  Electrical  Engineers I2mo,  i   50 

Morse's  Calculations  used  in  Cane-sugar  Factories. i6mo,  mor.  i  50 

*  Mu'r's  History  of  Chemical  Theories  and  Laws • ,8vo,  4  oo 

Mullik«n's  General  Method  for  the  Identification  of  Pure  Organic  Compounds. 

Vol.  I Large  Svo,  5  oo» 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores Svo,  2  oo> 

Ostwald's  Conversations  on  Chemistry.     Part  One.     (Ramsey.) I2mo,  i  50 

Part  Two.     (Turnbull.).  ......  i2mo,  2  oo> 

*  Palmer's  Practical  Test  Book  of  Chemistry i2mo,  i  co> 

*  Pauli's  Physical  Chemistry  in  the  Service  of  Medicine.     (Fischer.) .  .  .  .  I2mo,  i   25, 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

Svo,  paper,         50 
Tables   of  Minerals,  Including  the   Use    of  Minerals  and  Statistics  of 

Domestic  Production Svo,  i  oo 

Pictet's  Alkaloids  and  their  Chemical  Constitution.     (Biddle.) 8<ro,  5  oa 

Poole's  Calorific  Power  of  Fuels Svo,  3  oo 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis i2iro,  i  50 

*  Reisig's  Guide  to  Piece-dyeing Svo,  25  oo 

Richards  and  Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Standpoint.. 8  vo,  2  oo 

Ricketts  and  Miller's  Notes  on  Assaying Svo,  3  oo- 

Rideal's  Disinfection  and  the  Preservation  of  Food Svo,  4  oo 

Sewage  and  the  Bacterial  Purification  of  Sewage Svo,  4  oo 

Riggs's  Elementary  Manual  for  the  Chemical  Laboratory Svo,  i  25 

Robine  and  Lenglen's  Cyanide  Industry.  (Le  Clerc.) 8vo,  4  oo 

Ruddiman's  Incompatibilities  in  Prescriptions Svo,  2  oo 

Whys  in  Pharmacy J2mo,  i  00= 

5 


Ruer's  Elements  of  Metallography.     (Mathewson).      fin  Preparation.) 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,  2  50 

Schimpf's  Essentials  of  Volumetric  Analysis I2mo,  i   25 

*  Qualitative  Chemical  Analysis 8vo,  i   25 

Text-book  of  Volumetric  Analysis i2mo,  2  50 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students , .  .8vo,  2  50 

Spencer's  Handbook  for  Cane  Sugar  Manufacturers i6mo,  mor.  3  oo 

Handbook  for  Chemists  of  Beet-sugar  Houses i6mo,  mor.  3  oo 

Stockbridge's  Rocks  and  Soils 8vo,  2  50 

*  Tillman's  Descriptive  General  Chemistry 8vo,  3  oo 

*  Elementary  Lessons  in  Heat 8vo,  i  50 

Treadwell's  Qualitative  Analysis.     (Hall.) 8vo,  3  oo 

Quantitative  Analysis.     (Hall.) 8vo,  4  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Van  Deventer's  Physical  Chemistry  for  Beginners.     (Boltwood.) i2mo,  i  50 

Venable's  Methods  and  Devices  for  Bacterial  Treatment  of  Sewage 8vo,  3  oo 

Ward  and  Whipple's  Freshwater  Biology.     (In  Press.) 

Ware's  Beet-sugar  Manufacture  and  Refining.     Vol.  I Small  8vo,  4  oo 

Vol.  II SmallSvo,  5  co 

Washington's  Manual  of  the  Chemical  Analysis  of  Rocks 8vo,  2  oo 

*  Weaver's  Military  Explosives 8vo,  3  oo 

Wells's  Laboratory  Guide  in  Qualitative  Chemical  Analysis 8vo,  i  50 

Short  Course  in  Inorganic  Qualitative  Chemical  Analysis  for  Engineering 

Students i2mo,  i  50 

Text-book  of  Chemical  Arithmetic i2mo,  i  25 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

Wilson's  Chlorination  Process I2mo  i   53 

Cyanide  Processes i2mo  i  50 

Winton's  Microscopy  of  Vegetable  Foods 8vo  7  50 


CIVIL  ENGINEERING. 

BRIDGES  AND  ROOFS.     HYDRAULICS.     MATERIALS   OF    ENGINEER- 
ING.    RAILWAY   ENGINEERING. 

Baker's  Engineers'  Surveying  Instruments 12 mo,  3  oo 

Bixby's  Graphical  Computing  Table Paper  io.£X24i  inches.  25 

Breed  and  Hosmer's  Principles  and  Practice  of  Surveying 3vo,  3  oo 

*  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Canal   ...     8vo,  3  50 
Comstock's  Field  Astronomy  for  Engineers 8vc,  2  50 

*  Corthell's  Allowable  Pressures  on  Deep  Foundations ^ I2mo,  i  25 

CrandalPs  Text-book  on  Geodesy  and  Least  Squares 8vo,  3  oo 

Davis's  Elevation  and  Stadia  Tables 8vo,  i  oo 

Elliott's  Engineering  for  Land  Drainage i2mo,  i  50 

Practical  Farm  Drainage i2mo,  i  oo 

*Fiebeger's  Treatise  on  Civil  Engineering 8vo,  5  oo 

Flemer's  Phototopographic  Methods  and  Instruments 8vo,  5  oo 

Folwell's  Sewerage.     (Designing  and  Maintenance.) 8vo,  3  oo 

Freitag's  Architectural  Engineering 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Goodhue's  Municipal  Improvements 12010,  i  50 

Gore's  Elements  of  Geodesy 8vo,  2  50 

*  Hauch  and  Rice's  Tables  of  Quantities  for  Preliminary  Estimates, I2mo,  i  25 

Hayford's  Text-book  of  Geodetic  Astronomy 8vo,  3  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.  2  50 

Howe's  Retaining  Walls  for  Earth i2mo,  i  25 

6 


*  Ives's  Adjustments  of  the  Engineer's  Transit  and  Level i6mo,  Bds.  25 

Ives  and  Hilts's  Problems  in  Surveying i6mo,  mor.  i  50 

Johnson's  (J.  B.)  Theory  and  Practice  of  Surveying Small  8vo,  4  oo 

Johnson's  (L.  J.)  Statics  by  Algebraic  and  Graphic  Methods 8vo,  2  oo 

Kinnicutt,  Winslow  and  Pratt's  Purification  of  Sewage.     (In  Preparation). 
Laplace's    Philosophical    Essay    on    Probabilities.       (Truscott    and   Emory.) 

1 2 mo,  2  oo 

Mahan's  Descriptive  Geometry 8vo,  i  50 

Treatise  on  Civil  Engineering.     (1873.)     (Wood.) 8vo,  5  oo 

Merriman's  Elements  of  Precise  Surveying  and  Geodesy 8vo,  2  50 

Merriman  and  Brooks's  Handbook  for  Surveyors i6mo,  mor.  2  oo 

Morrison's  Elements  of  Highway  Engineering.       (In  Press.) 

Nugent's  Plane  Surveying 8vo,  3  50 

Ogden's  Sewer  Design I2mo,  2  oo 

Parsons's  Disposal  of  Municipal  Refuse 8vo,  2  oo 

Patton's  Treatise  on  Civil  Engineering 8vo,  half  leather,  7  50 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Rideal's  Sewage  and  the  Bacterial  Purification  of  Sewage 8vo,  4  oo 

Riemer's  Shaft-sinking  under  Difficult  Conditions.     (Corning  and  Peele.).  .8 vo,  3  oo 

Siebert  and  Biggin's  Modern  Stone-cutting  and  Masonry 8vo,  I  50 

Smith's  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Soper's  Air  and  Ventilation  of  Subways.     (In  Press.) 

Tracy's  Plane  Surveying I6mo,  mor.  3  oo 

*  Trautwine's  CivM  Engineer's  Pocket-book i6mo,  mor.  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

Methods  and  Devices  for  Bacterial  Treatment  of  Sewage 8vo,  3  oo 

Wait's  Engineering  and  Architectural  Jurisprudence 8vo,  6  oo 

Sheep,  6  50 

Law  of  Contracts 8vo,  3  oo 

Law  of  Operations  Preliminary  io  Construction  in  Engineering  and  Archi- 
tecture  8vo,  5  oo 

Sheep,  5  50 

Warren's  Stereotomy — Problems  in  Stone-cutting 8vo,  2  50 

*  Waterbury's  Vest-Pocket  Hand-book   of    Mathematics   for   Engineers. 

2 JX si  inches,  mor.  i  oo 
Webb's  Problems  in  the  Use  and  Adjustment  of  Engineering  Instruments. 

i6mo,  mor.  i  25 

Wilson's  Topographic  Surveying 8vo,  3  50 

BRIDGES  AND  ROOFS. 

Boiler's  Practical  Treatise  on  the  Construction  of  Iron  Highway  Bridges .  .  8vo,  2  bo 

Burr  and  Falk's  Design  and  Construction  of  Metallic  Bridges 8vo,  5  oo 

Influence  Lines  for  Bridge  and  Roof  Computations 8vo,  3  oo 

Du  Bois's  Mechanics  of  Engineering.     Vol.  II Small  4to,  io  oo 

Foster's  Treatise  on  Wooden  Trestle  Bridges 4to,  5  oo 

Fowler's  Ordinary  Foundations 8vo,  3  50 

French  and  Ives's  Stereotomy 8vo,  2  50 

Greene's  Arches  in  Wood,  Iron,  and  Stone. 8vo,  2  50 

Bridge  Trusses 8vo,  2  50 

Roof  Trusses 8vo,  i  25 

Grimm's  Secondary  Stresses  in  Bridge  Trusses 8vo,  2  50 

Heller's  Stresses  in  Structures  and  the  Accompanyin-  Deformations 8vo, 

Howe's  Design  of  Simple  Roof-trusses  in  Wood  and  Steel 8vo,  2  oo 

Symmetrical  Masonry  Arches 8vo,  2  50 

Treatise  on  Arches 8vo,  4  oo 

Johnson,  Bryan,  and  Turneaure's  Theory  and  Practice  in  the  Designing  of 

Modern  Framed  Structures .» Small  4to,  io  oo 

7 


Merriman  and  Jacoby's  Text-book  on  Roofs  and  Bridges: 

Part  I.      Stresses  in  Simple  Trusses 8vo,  2  50 

Part  II.     Graphic  Statics 8vo,  2  50 

Part  III.  Bridge  Design 8vo,  2  50 

Part  IV.    Higher  Structures 8vo,  2  50 

Morison's  Memphis  Bridge Oblong  4to,  10  oo 

Sondericker's  Graphic  Statics,  with  Applications  to  Trusses,  Beams,  and  Arches. 

8vo,  2  oo 

Waddell's  De  Pontibus,  Pocket-book  for  Bridge  Engineers  ......    i6mo,  mor,  2  oo 

*          Specifications  for  Steel  Bridges i2mo,  50 

Waddell  and  Harrington's  Bridge  Engineering.     (In  Preparation.) 

Wright's  Designing  of  Draw-spans.     Two  parts  in  one  volume 8vo,  3  50 


HYDRAULICS. 

Barnes's  Ice  Formation 8vo,  3  oo 

Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein  Issuing  from 

an  Orifice.     (Trautwine.) 8vo,  2  oo 

Bovey's  Treatise  on  Hydraulics 8vo,  5  oo 

Church's  Diagrams  of  Mean  Velocity  of  Water  in  Open  Channels. 

Oblong  4to,  paper,  i  50 

Hydraulic  Motors ...  8vo,  2  oo 

Mechanics  of  Engineering 8vo,  6  oo 

Coffin's  Graphical  Solution  of  Hydraulic  Problems i6mo,  morocco,  2  50 

blather's  Dynamometers,  and  the  Measurement  of  Power i2mo,  3  oo 

FolwelTs  Water-supply  Engineering 8vo,  4  oo 

Frizell's  Water-power 8vo,  5  oo 

Fuertes's  Water  and  Public  Health i2mo,  i  50 

Water-filtration  Works i2mo,  2  50 

Ganguillet  and  Kutter's  General  Formula  for  the  Uniform  Flow  of  Water  in 

Rivers  and  Other  Channels.     (Hering  and  Trautwine.) 8vo,  4  oo 

Hazen's  Clean  Water  and  How  to  Get  It Large  I2mo,  i  5o 

Filtration  of  Public  Water-supplies 8v,o,  3  oo 

Hazlehurst's  Towers  and  Tanks  for  Water-works 8vo,  2  50 

Herschel's  115  Experiments  on  the  Carrying  Capacity  of  Large,  Riveted,  Metal 

Conduits 8vo,  2  oo 

Hoyt  and  Grover's  River  Discharge 8vo,  2  oo 

Hubbard  and  Kiersted's  Water- works  Management  and  Maintenance. . . '.  .8vo,  4  co 

*  Lyndon's  Development  and  Electrical  Distribution  of  Water  Power.  .  .  .8vo,  3  oo 
Mason'^  Water-supply.     (Considered  Principally  from  a  Sanitary  Standpoint.) 

8vo,  4  oo 

Merriman's  Treatise  on  Hydraulics 8vo,  5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,  4  oo 

MoHtor's  Hydraulics  of  Rivers,  Weirs  and  Sluices.     (In  Press  ) 

Schuyler's   Reservoirs   for   Irrigation,   Water-power,   and   Domestic   Water- 
supply Large  8vo,  5  oo 

*  Thomas  and  Watt's  Improvement  of  Rivers 4to,  6  oo 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Wegmann's  Design  and  Construction  of  Dams.     5th  Ed.,  enlarged 410,  6  oo 

Water-supply  of  the  City  of  New  York  from  1658  to  1895 4to,  10  oo 

Whipple's  Value  of  Pure  Water Large  i2mo,  i  oo 

Williams  and  Hazen's  Hydraulic  Tables 8vo,  i  50 

Wilson's  Irrigation  Engineering Small  8vo,  4  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Turbines • 8vo,  2  50 

8 


MATERIALS  OF  ENGINEERING. 

Baker's  Roads  and  Pavements 8vo,  5  oo 

Treatise  on  Masonry  Construction 8vo,  5  oo 

Birkmire's  Architectural  Iron  and  Steel 8vo,  3  50 

Compound  Riveted  Girders  as  Applied  in  Buildings 8vo,  2  oo 

Black's  United  States  Public  Works Oblong  4to,  5  oo 

Bleininger's  Manufacture  of  Hydraulic  Cement. '    (In  Preparation.) 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Byrne's  Highway  Construction 8vo,  5  oo 

Inspection  of  the  Materials  and  Workmanship  Employed  in  Construction. 

i6mo,  3  oo 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

Du  Bois's  Mechanics  of  Engineering. 

Vol.    I.  Kinematics,  Statics,  Kinetics Small  4to,  7  50 

Vol.  II.  The  Stresses  in  Framed  Structures,  Strength  of  Materials  and 

Theory  of  Flexures Small  4to,  10  oo 

*EckeI's  Cements,  Limes,  and  Plasters 8vo,  6  oo 

Stone  and  Clay  Products  used  in  Engineering.     (In  Preparation.) 

Fowler's  Ordinary  Foundations 8vo,  3  50 

Graves's  Forest  Mensuration 8vo,  4   oo 

Green's  Principles  of  American  Forestry i2mo,  i   «;o 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Holly  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments  and  Varnishes 

Large  i2mo,  2  50 

Johnson's  Materials  of  Construction Large  8vo,  6  oo 

Keep's  Cast  Iron 8vo,  2  50 

Kidder's  Architects  and  Builders'  Pocket-book i6mo,  5  oo 

Lanza's  Applied  Mechanics 8vo,  7  50 

Maire's  Modern  Pigments  and  their  Vehicles      . I2mo,  2  oo 

Martens's  Handbook  on  Testing  Materials.     (Henning.)     2  vols 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

*  Strength  of  Materials i2mo,  i  oo 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Patton's  Practical  Treatise  on  Foundations 8vo,  5  oo 

Rice's  Concrete  Block  Manufacture 8vo,  2  oo 

Richardson's  Modern  Asphalt  Pavements.  . ,                                8vo,  3  oo 

Richey's  Handbook  for  Superintendents  of  Co     n      aon i6mo,  mor.,  400 

*  Ries's  Clays:  Their  Occurrence,  Properties,  ana  Jses 8vo,  5  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  arA  Varnish 8vo,  3  oo 

*Schwarz's  Longleaf  Pine  in  Virgin  Forest,., i2tno,  i   25 

Snow's  Principal  Species  of  Wood 8vo,  3  50 

Spalding's  Hydraulic  Cement i2mo,  2  oo 

Text-book  on  Roads  and  Pavements i2mo,  2  oo 

Taylor  and  Thompson's  Treatise  on  Concrete,  Plain  and  Reinforced 8vo,  5  oo 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

Part  I.     Non-metallic  Materials  of  Engineering  and  Metallurgy 8vo,  2  oo 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Tillson's  Street  Pavements  and  Paving  Materials 8vo,  4  oo 

Turneaure  and  Maurer's  Principles  of  Reinforced  Concrete  Construction-.  .8vo,  3  oo 
Wood's  (De  V.)  Treatise  on  the  Resistance  of  Materials,  and  an  Appendix  on 

the  Preservation  of  Timber 8vo,  2  oo 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo 

9 


RAILWAY  ENGINEERING. 

Andrews's  Handbook  for  Street  Railway  Engineers 3x5  inches,  mor.     i  25 

Berg's  Buildings  and  Structures  of  American  Railroads 4*0,    5  oo 

Brooks's  Handbook  of  Street  Railroad  Location i6mo,  mor. 


Butt's  Civil  Engineer's  Field-book i6mo,  mor. 

Crandall's  Railway  and  Other  Earthwork  Tables .  8vo, 

Transition  Curve i6mo,  mor. 

*  Crockett's  Methods  for  Earthwork  Computations 8vo, 


50 
50 
50 
50 
50 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book i6mo,  mor.  5  oo 

Dredge's  History  of  the  Pennsylvania  Railroad:    (1879) Paper,  5  oo 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Godwin's  Railroad  Engineers'  Field-book  and  Explorers'  Guide.  .  .  i6mo,  mor.  2  50 
Hudson's  Tables  for  Calculating  the  Cubic  Contents  of  Excavations  and  Em- 
bankments  8vo,  i  oo 

Ives   and  Hilts'c   Problems   in  Surveying,  Railroad   Surveying  and   Geodesy 

i6mo,  mor.  i   50 

Molitor  and  Beard's  Manual  for  Resident  Engineers i6mo,  i  oo 

Nagle's  Field  Manual  for  Railroad  Engineers i6mo,  mor.  3  oo 

Philbrick's  Field  Manual  for  Engineers i6mo,  mor.  3  oo 

Raymond's  Railroad  Engineering.     3  volumes. 

Vol.      I.  Railroad  Field  Geometry.     (In  Preparation.) 

Vol.    II.  Elements  of  Railroad  Engineering 8vo,  3  50 

Vol  III.  Railroad  Engineer's  Field  Book.     (In  Preparation.) 

Searles's  Field  Engineering i6mo,  mor.  3  oo 

Railroad  Spiral i6mo,  mor.  i  50 

Taylor's  Prismoidal  Formulae  and  Earthwork 8vo,  i  50 

*Trautwine's  Field  Practice  of  Laying   Out  Circular  Curves   for  Railroads. 

i2mo.  mor,  2  50 

*  Method  of  Calculating  the  Cubic  Contents  of  Excavations  and  Embank- 

ments by  the  Aid  of  Diagrams 8vo,  2  oo 

Webb's  Economics  of  Railroad  Construction Large  i2mo,  2  50 

Railroad  Construction : i6mo,  mor.  5  oo 

Wellington's  Economic  Theory  of  the  Location  of  Railways Small  8vo,  5  oo 

DRAWING. 

Barr's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "                   "              "            Abridged  Ed 8vo,  150 

Coolidge's  Manual  of  Drawing 8vo,  paper,  i  oo 

Cooiidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  Engi- 
neers  Oblong  4to,  2  50 

Durley's  Kinematics  of  Machines 8vo,  4  oo 

Emch's  Introduction  to  Projective  Geometry  and  its  Applications Svo,  2  50 

Hill's  Text-book  on  Shades  and  Shadows,  and  Perspective Svo,  2  oo 

Jamison's  Advanced  Mechanical  Drawing Svo,  2  oo 

Elements  of  Mechanical  Drawing Svo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery Svo,  i  50 

Part  II.    Form,  Strength,  and  Proportions  of  Parts Svo,  3  oo 

MacCord's  Elements  of  Descriptive  Geometry Svo,  3  oc 

Kinematics;   or,  Practical  Mechanism Svo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams Svo,  i  50 

McLeod's  Descriptive  Geometry Large  tamo,  i  50 

*  Mahan's  Descriptive  Geometry  and  Stone-cutting Svo,  i  50 

Industrial  Drawing.     (Thompson.) Svo,  3  50 

10 


Moyer's  Descriptive  Geometry 8vo,  2  oo 

Reed's  Topographical  Drawing  and  Sketching 4to,  5  oo 

Reid's  Course  in  Mechanical  Drawing 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (R.  S.)  Manual  of  Topographical  Drawing.     (McMillan.) 8vo,  2  50 

Smith  (A.  W.)  and  Marx's  Machine  Design. » 8vo,  3  oo 

*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo,  i   25 

Warren's  Drafting  Instruments  and  Operations i2mo,  i  25 

Elements  of  Descriptive  Geometry,  Shadows,  and  Perspective 8vo,  3  50 

Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

Elements  of  Plane  and  Solid  Free-hand  Geometrical  Drawing.  .  .  .  i  .2mo,  i  oo 

General  Problems  of  Shades  and  Shadows 8vo,  3  oo 

Manual  of  Elementary  Problems  in  the  Linear  Perspective  of  Form  and 

Shadow i2mo,  i  oo 

Manual  of  Elementary  Projection  Drawing I2mo,  i  50 

Plane  Problems  in  Elementary  Geometry i2mo,  i  25 

Problems,  Theorems,  and  Examples  in  Descriptive  Geometry 8vo,  2  50 

Weisbach's    Kinematics    and    Power    of    Transmission.        (Hermann    and 

Klein.) 8vo,  5  oo 

Wilson's  (H.  M.)  Topographic  Surveying 8vo,  3  50 

Wilson's  (V.  T.)  Free-hand  Lettering 8vo,  i  oo 

Free-hand  Perspective 8vo,  2  50 

Woolf's  Elementary  Course  in  Descriptive  Geometry Large  8vo,  3  oo 

ELECTRICITY  AND  PHYSICS. 

*  Abegg's  Theory  of  Electrolytic  Dissociation,     (von  Ende.) I2mo,  i   25 

Andrews's  Hand-Book  for  Street  Railway  Engineering 3X5  inches,  mor.,  i  25 

Anthony  and  Brackett's  Text-book  of  Physics.     (Magie.) Large  i2mo,  3  oo 

Anthony's  Lecture-notes  on  the  Theory  of  Electrical  Measurements.  .  .  .  i2mo,  i  oo 

Benjamin's  History  of  Electricity 8vo,  3  oo 

Voltaic  Cell 8vo,  3  oo 

Betts's  Lead  Refining  and  Electrolysis 8vo,  .4  oo 

Classen's  Quantitative  Chemical  Analysis  by  Electrolysis.     (Boltwood.).8vo,  3  oo 

*  Collins's  Manual  of  Wireless  Telegraphy i2mo,  i  50 

Mor.  2  oo 

Crehore  and  Squier's  Polarizing  Photo-chronograph 8vo,  3  oo 

*  Danneel's  Electrochemistry.     (Merriam.) 12010,  i   25 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book i6mo,  mor  5  oo 

Dolezalek's  Theory  of  the  Lead  Accumulator  (Storage  Battery),    (von  Ende.) 

12010,      2    50 

Duhem's  Thermodynamics  and  Chemistry.     (Burgess.) 8vo,  4  co 

Flather's  Dynamometers,  and  the  Measurement  of  Power 12010,  3  oo 

Gilbert's  De  Magnete.     (Mottelay.) 8vo,  2  50 

*  Hanchett's  Alternating  Currents I2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6m'o,  mor.  2  50 

Hobart  and  Ellis 's  High-speed  Dynamo  Electric  Machinery.     (In  Press.) 

Holman's  Precision  of  Measurements 8vo,  2  oo 

Telescopic   Mirror-scale  Method,  Adjustments,  and  Tests.  ..  .Large  8vo,  75 

*  Karapetoff  s  Experimental  Electrical  Engineering 8vo,  6  oo 

Kinzbrunner's  Testing  of  Continuous-current  Machines 8vo,  2  oo 

Landauer's  Spectrum  Analysis.     (Tingle.) 8vo,  3  oo 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.)  I2mo,  3  oo 

Lob's  Electrochemistry  of  Organic  Compounds.     (Lorenz.) 8vo,  3  oo 

*  London's  Development  and  ElectricJl  Distribntion  of  Water  Power  .  . .  .8vo,  3  oo 

*  Lyons's  Treatise  on  Electromagnetic  Phenomena.   Vols.  I.  and  II.  8vo,  each,  6  oo 

*  Michie's  Elements  of  Wave  Motion  Relating  to  Sound  and  Light 8vo,  4  oo 

11 


Morgan's  Outline  of  the  Theory  of  Solution  and  its  Results i2mo,  i  oo 

*  Phys'.cal  Chemistry  for  Electrical  Engineers i2mo,  i  50 

Niauclet's  Elementary  Treatise  en  Electric  Batteries.     (Fishback) .  .  .  .  i2mo.  a   50 

*  Norris's  Introduction  to  the  Study   of  Electrical  Engineering Svo,  2  50 

*  Parshall  and  Hobart's  Electric  Machine  Design 4to,  half  morocco,  12   50 

Reagan's  Locomotives:    Simple,  Compound,  and  Electric.      New  Edition. 

Large  i2mo,  3  50 

*  Rosenberg's  Electrical  Engineering.      (Haldane  Gee — Kinzbrunner.).  .  .8vo,  2  oo 

Ryan,  Norris,  and  Hoxie's  Electrical  Mechinery.     Vol.  1 8vo,  2  50 

S;happer's  Laboratory  Guide  for  Students  in  Physical  Chemistry i2mo,  i  oo 

Thurston's  Stationary  Steam-engines 8vo,  2  50 

*  Tillman's  Elementary  Lessons  in  Heat 8vo,  i   50 

Tory  and  Pitcher's  Manual  of  Laboratory  Physics Large  I2mo,  2  oo 

Ulke's  Modern  Electrolytic  Copper  Refining Svo,  3  oo 

LAW. 

*  Davis's  Elements  of  Law Svo,  2  50 

*  Treatise  on  the  Military  Law  of  United  States Svo,  7  oo 

*  Sheep,  7  50 

*  Dudley's  Military  Law  and  the  Procedure  cf  Courts-martial  .  .  .  .Large  i2mo,  2  50 

Manual  for  Courts-martial i6mo,  mor.  i  50 

Wait's  Engineering  and  Architectural  Jurisprudence « Svo,  6  oo 

Sheep,  6  50 

Law  of  Contracts Svo,  3  oo 

Law  of  Operations  Preliminary  to  Construction  in  Engineering  and  Archi- 
tecture  Svo  5  oo 

Sheep,  5  50 
MATHEMATICS. 

Baker's  Elliptic  Functions Svo, 

Briggs's  Elements  of  Plane  Analytic  Geometry.    (Bocher) i2mo, 

*  Buchanan's  Plane  and  Spherical  Trigonometry Svo, 

Byerley's  Harmonic  Functions Svo, 

Chandler's  Elements  of  the  Infinitesimal  Calculus i2mo, 

Compton's  Manual  of  Logarithmic  Computations i2mo, 

Davis's  Introduction  to  the  Logic  of  Algebra Svo, 

*  Dickson's  College  Algebra Large  i2mo, 

*  Introduction  to  the  Theory  of  Algebraic  Equations Large  i2mo, 

Etnch's  Introduction  to  Projective  Geometry  and  its  Applications Svo, 

Fiske's  Functions  of  a  Complex  Variable Svo, 

Halsted's  Elementary  Synthetic  Geometry Svo, 

Elements  of  Geometry Svo,  75 

*  Rational  Gsometry .- 12010,  50 

Hyde's  Grassmann's  Space  Analysis Svo,  oo 

*  Jonnson's  (J    B  )  Three-place  Logarithmic  Tables:  Vest-pocket  size,  paper,  15 

100  copies,  5  oo 

*  Mounted  on  heavy  cardboard,  8X 10  inches,  25 

10  copies,  2  oo 
Johnson's  (W.  W.)  Abridged  Editions  of  Differential  and  Integral  Calculus 

Large  i2mo,  i  vol.  2  50 

Curve  Tracing  in  Cartesian  Co-ordinates i2mo,  i  oo 

Differential  Equations Svo,  i  oo 

Elementary  Treatise  r«a  Differential  Calculus.     (In  Press.) 

Elementary  Treatise  on  the  Integral  Calculus Large  i2mos  i  50 

*  Theoretical  Mechanics i2mo,  3  oo 

Theory  of  Errors  and  the  Method  of  Least  Squares I2mo,  i   50 

Treatise  on  Differential  Calculus .  .  .  .  « Large  i2mo,  3  oo 

Treatise  on  the  Integral  Calculus Large  i2mo,  3  oo 

Treatise  on  Ordinary  and  Partial  Differential  Equations.  .Large  i2mo,  3  50 

12 


taplace's  Philosophical  Essay  on  Probabilities.     (Truscott  and  Emory. ).i2mo,     2  oo 

*  Ludlow  and  Bass's  Elements  of  Trigonometry  and  Logarithmic  and  Other 

Tables 8vo,     3  oo 

Trigonometry  and  Tables  published  separately Each,     2  oo 

*  Ludlow's  Logarithmic  and  Trigonometric  Tables 8vo,     i   oo 

Macfarlane's  Vector  Analysis  and  Quaternions 8vo,     i  oo 

McMahon's  Hyperbolic  Functions 8vo,     i  oo 

Manning's  IrrationalNumbers  and  their  Representation  bySequences  and  Series 

i2mo,     i   25 
Mathematical  Monographs.     Edited  by  Mansfield  Merriman  and  Robert 

S.  Woodward. Octavo,  each     i  oo 

No.  i.  History  of  Modern  Mathematics,  by  David  Eugene  Smith. 
No.  2.  Synthetic  Projective  Geometry,  by  George  Bruce  Halsted. 
No.  3.  Determinants,  by  Laenas  Gifford  Weld.  No.  4.  Hyper- 
bolic Functions,  by  James  McMahon.  Ko.  ~>.  Harmonic  Func- 
tions, by  William  E.  Byerly.  No.  6.  Grassmann's  Space  Analysis, 
by  Edward  W.  Hyde.  No.  7.  Probability  and  Theory  of  Errors, 
by  Robert  S.  Woodward.  No.  8.  Vector  Analysis  and  Quaternions, 
by  Alexander  Macfarlane.  No.  9.  Differential  Equations,  by 
William  Woolsey  Johnson.  No.  10.  The  Solution  of  Equations, 
by  Mansfield  Merriman.  No.  n.  Functions  of  a  Complex  Variable, 
by  Thomas  S.  Fiske. 

Maurer's  Technical  Mechanics 8vo,    4  oo 

Meulman's  Method  of  Least  Squares 8vo,    2  oo 

Solution  of  Equations 8vo,     i  oo 

Rice  and  Johnson's  Differential  and  Integral  Calculus.     2  vols.  in  one. 

Large  12 mo,     i  50 

Elementary  Treatise  on  the  Differential  Calculus Large  i2mo,     3  oo 

Smith's  History  of  Modern  Mathematics 8vo,     i  oo 

*  Veblen  and  Lennes's  Introduction  to  the  Real  Infinitesimal  Analysis  of  One 

Variable 8vo,    2  oo 

*  Waterbury's  Vest  Pocket  Hand-Book  of  Mathematics  for  Engine  rs. 

2-|X5i  inches,  mor.,     i  oo 

Weld's  Determinations 8vo,    i  co 

Wood's  Elements  of  Co-ordinate  Geometry 8vo,    2  oo 

Woodward's  Probability  and  Theory  of  Errors 8vo,    i  oo 

MECHANICAL  ENGINEERING. 

MATERIALS   OF    ENGINEERING,   STEAM-ENGINES  AND  BOILERS. 

Bacon's  Forge  Practice i2mo,  i  50 

Baldwin's  Steam  Heating  for  Buildings I2mo,  2  50 

Bair's  Kinematics  of  Machinery 8vo,  2  50 

*  Bartlett's  Mechanical  Drawing 8vo,  3  oo 

*  "  "  "        Abridged  Ed 8vo,    i  50 

Benjamin's  Wrinkles  and  Recipes i2mo,    2  oo 

*  Burr's  Ancient  and  Modern  Engineering  and  the  Isthmian  Canal 8vo,    3  50 

Carpenter's  Experimental  Engineering 8vo,    6  oo 

Heating  and  Ventilating  Buildings 8vo,  4  oo 

Clerk's  Gas  and  Oil  Engine Large  12010,  4  oo 

Compton's  First  Lessons  in  Metal  Working i2mo,  50 

Compton  and  De  Groodt's  Speed  Lathe 12mo,  50 

Coolidge's  Manual  of  Drawing 8vo,  paper,  oo 

Coolidge  and  Freeman's  Elements  of  General  Drafting  for  Mechanical  En- 
gineers   Oblong  4to,  50 

Cromwell's  Treatise  on  Belts  and  Pulleys .. i2mo,  50 

Treatise  on  Toothed  Gearing I2mo,  50 

Durley's  Kinematics  of  Machines ,8vo,  4  oo 

13 


Flather's  Dynamometers  and  the  Measurement  of  Power i2mo,  3  oo 

Rope  Driving i2mo,  2  o° 

Gill's  Gas  and  Fuel  Analysis  for  Engineers i2mo,  i  25 

Goss'  -,  Locomotive  Sparks 8vo,  2  oo 

Hall's  Car  Lubrication I2mo,  i  oo 

Bering's  Ready  Reference  Tables  (Conversion  Factors) i6mo,  mor.,  2  50 

Hobart  and  Elus's  High  Speed  Dynamo  Electric  Machinery.     (In  Press.) 

Button's  Gas  Engine 8vo,  5  oo 

Jamison's  Advanced  Mechanical  Drawing 8vo,  2  oo 

Elements  of  Mechanical  Drawing 8vo,  2  50 

Jones's  Machine  Design: 

Part  I.     Kinematics  of  Machinery 8vo,  i  50 

Part  II.     Form,  Strength,  and  Proportions  of  Parts 8vo,  3  oo 

Kent's  Mechanical  Engineers'  Pocket-book ..i6mo,  mor  ,  5  oo 

Kerr's  Power  and  Power  Transmission 8vo,  2  oo 

Leonard's  Machine  Shop  Tools  and  Methods! 8vo,  4  oo 

*  Lorenz's  Modern  Refrigerating  Machinery.    (Pope,  Haven,  and  Dean.) .  .8vo,  4  oo 
MacCord's  Kinematics;   or,  Practical  Mechanism 8vo,  5  oo 

Mechanical  Drawing 4to,  4  oo 

Velocity  Diagrams 8vo,  i  50 

MacFar land's  Standard  Reduction  Factors  for  Gases 8vo,  i  50 

Mahan's  Industrial  Drawing.   •(Thompson.) 8vo,  3  50 

*  Parshall  and.Hobart's  Electric  Machine  Design Small  4to,  half  leather,  12  50 

Peele's  Compressed  Air  Plant  for  Mines.     (In  Press.) 

Poole's  Calorific  Power  of  Fuels 8vo,  3  oo 

*  Porter's  Engineering  Reminiscences,  1855  to  1882 8vo,  3  oo 

Reid's  Course  in  Mechanical  Drawing t 8vo,  2  oo 

Text-book  of  Mechanical  Drawing  and  Elementary  Machine  Design. 8vo,  3  oo 

Richard's  Compressed  Air i2mo,  i  50 

Robinson's  Principles  of  Mechanism 8vo,  3  oo 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,  3  oo 

Smith's  (O.)  Press-working  of  Metals 8vo,  3  oo 

Smith  (A.  W.)  and  Marx's  Machine  Design 8vo,  3  oo 

Thurston's  Animal  as  a  Machine  and  Prime  Motor,  and  the  Laws  of  Energetics. 

i2mo,  i  oo 

Treatise  on  Friction  and  Lost  Work  in  Machinery  and  Mill  Work...  8vo,  3  oo 

Tillson's  Complete  Automobile  Instructor i6mo,  i  50 

mor.,  2  oo 

*  Titsworth's  Elements  of  Mechanical  Drawing Oblong  8vo,  i   25 

Warren's  Elements  of  Machine  Construction  and  Drawing 8vo,  7  50 

*  Waterbury's  Vest  Pocket  Hand  Book  of  Mathematics  for  Engineers. 

2jXsHnches,  mor.,  i  oo 
Weisbach's    Kinematics    and    the    Power    of    Transmission.     (Herrmann — 

Klein.) 8vo,  5  oo 

Machinery  of  Transmission  and  Governors.     (Herrmann — Klein.).  .8vc,  5  oo 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  oo 

Wood's  Turbines 8vo,  2  50 

MATERIALS  OF  ENGINEERING. 

*  Bovey's  Strength  of  Materials  and  Theory  of  Structures 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  the  Materials  of  Engineering 8vo,  7  50 

Church's  Mechanics  of  Engineering 8vo,  6  oo 

*  Greene's  Structural  Mechanics 8vo,  2  50 

Holley  and  Ladd's  Analysis  of  Mixed  Paints,  Color  Pigments,  and  Varnishes. 

Large  i2mo,  2  50 

Johnson's  Materials  of  Construction 8vo,  6  oo 

Keep's  Cast  Iron 8vo,  2  50 

Lanza's  Applied  Mechanics 8vo,  7  50 

14 


Maire's  Modern  Pigments  and  their  Vehicles i2mo,  2  oo 

Martens's  Handbook  on  Testing  Materials.     (Henning.) 8vo,  7  50 

Maurer's  Technical  Mechanics 8vo,  4  oo 

Merriman's  Mechanics  of  Materials 8vo,  5  oo 

*         Strength  of  Materials I2mo,  i  oo 

Metcalf's  Steel.     A  Manual  for  Steel-users i2mo,  2  oo 

Sabin's  Industrial  and  Artistic  Technology  of  Paints  and  Varnish 8vo,  3  oo 

Smith's  Materials  of  Machines I2mo,  i  oo 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  oo 

Part  I.     Non-metallic  Materials  of  Engineering,  see  Civil  Engineering, 
page  9. 

Part  II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Wood's  (De  V.)  Elements  of  Analytical  Mechanics 8vo,  3  oo 

Treatise  on    the    Resistance    of    Materials  and   an  Appendix  on  the 

Preservation  of  Timber 8vo,  2  oo 

Wood's  (M.  P.)  Rustless  Coatings:    Corrosion  and  Electrolysis  of  Iron  and 

Steel 8vo,  4  oo 

STEAM-ENGINES  AND  BOILERS. 

Berry's  Temperature-entropy  Diagram I2mo,  i  25 

Carnot's  Reflections  on  the  Motive  Power  of  Heat.     (Thurston.) i2mo,  i  50 

Chase'.s  Art  of  Pattern  Making i2mo,  2  50 

Creighton's  Steam-engine  and  other  Heat-motors 8vo,  5  oo 

Dawson's  "Engineering"  and  Electric  Traction  Pocket-book. . .  .i6mo,  mor.,  5  oo 

Ford's  Boiler  Making  for  Boiler  Makers i8mo,  i  oo 

Goss's  Locomotive  Performance ....    8vo,  5  oo 

Hemenway's  Indicator  Practice  and  Steam-engine  Economy i2mo,  2  oo 

Button's  Heat  and  Heat-engines 8vo,  5  oo 

Mechanical  Engineering  of  Power  Plants 8vo,  5  oo 

Kent's  Steam  boiler  Economy 8vo,  4  oo 

Kneass's  Practice  and  Theory  of  the  Injector 8vo,  i  50 

MacCord's  Slide-valves 8vo,  2  oo 

Meyer's  Modern  Locomotive  Construction 4to,  10  oo 

Moyer's  Steam  Turbines.     (Tn  Press.) 

Peabody's  Manual  of  the  Steam-engine  Indicator 12 mo,  i  50 

Tables  of  the  Properties  of  Saturated  Steam  and  Other  Vapors   8vo,  i  oo 

Thermodynamics  of  the  Steam-engine  and  Other  Heat-engines 8vo,  5  oo 

Valve-gears  for  Steam-engines 8vo,  2  50 

Peabody  and  Miller's  Steam-boilers 8vo,  4  oo 

Pray's  Twenty  Years  with  the  Indicator Large  8vo,  2  50 

Pupin's  Thermodynamics  of  Reversible  Cycles  in  Gases  and  Saturated  Vapors. 

(Osterberg.) I2mo,  i  25 

Reagan's  Locomotives:    Simple,  Compound,  and  Electric.     New  Edition. 

Large  12 mo,  3  50 

Sinclair's  Locomotive  Engine  Running  and  Management i2mo,  2  oo 

Smart's  Handbook  of  Engineering  Laboratory  Practice I2mo,  2  50 

Snow's  Steam-boiler  Practice 8vo,  3  oo 

Spangler's  Notes  on  Thermodynamics I2mo,  i  oo 

Valve-gears i 8vo,  2  50 

Spangler,  Greene,  and  Marshall's  Elements  of  Steam-engineering 8vo,  3  oo 

Thomas's  Steam-turbines 8vo,  4  oo 

Thurston's  Handbook  of  Engine  and  Boiler  Trials,  and  the  Use  of  the  Indi- 
cator and  the  Prony  Brake 8vo,  5  oo 

Handy  Tables .8vo,  i  50 

Manual  of  Steam-boilers,  their  Designs,  Construction,  and  Operation..8vo,  5  oo 

15 


Thurston's  Manual  of  the  Steam-engine 2  vols.,  8vo,  10  oo> 

Part  I.     History,  Structure,  and  Theory 8vo,  6  oo 

Part  II.     Design,  Construction,  and  Operation 8vo,  6  oo 

Stationary  Steam-engines 8vo,  2  50 

Steam-boiler  Explosions  in  Theory  and  in  Practice 12mo,  I  so 

Wehrenfenning's  Analysis  and  Softening  of  Boiler  Feed-water  (Patterson)   8vo,  4  oo 

Weisbach's  Heat.  Steam,  and  Steam-engines.     (Du  Bois.) 8vo,  5  oo 

Whitham's  Steam-engine  Design 8vo,  5  oo 

Wood's  Thermodynamics,  Heat  Motors,  and  Refrigerating  Machines.  .  .8vo,  4  oa 

MECHANICS  PURE  AND  APPLIED. 

Church's  Mechanics  of  Engineering 8vo,    6  oa 

Notes  and  Examples  in  Mechanics 8vo,    2  oo 

Dana's  Text-book  of  Elementary  Mechanics  for  Colleges  and  Schools.  .i2mo,     i  50 
Du  Bois's  Elementary  Principles  of  Mechanics: 

Vol.      I.     Kinematics 8vo,    3  50 

Vol.    II.     Statics 8vo,    4  oo 

Mechanics  of  Engineering.     Vol.    I Small  4to,     7  50 

Vol.  II Small  4to,  10  oo 

*  Greene's  Structural  Mechanics 8vo,    2  50 

James's  Kinematics  of  a  Point  and  the  Rational  Mechanics  of  a  Particle. 

Large  12mo,     2  oo 

*  Johnson's  (W.  W.)  Theoretical  Mechanics 12mo,    3  oo 

Lanza's  Applied  Mechanics 8vo,    7  50 

*  Martin's  Text  Book  on  Mechanics,  Vol.  I,  Statics 12mo,     i   25 

*  Vol.  2,  Kinematics  and  Kinetics  .  .I2mo,     1  50 
Maurer's  Technical  Mechanics 8vo,    4  oo 

*  Merriman's  Elements  of  Mechanics 12mo,     i  oo 

Mechanics  of  Materials 8vo,    5  oo 

*  Michie's  Elements  of  Analytical  Mechanics 8vo,    4  oo 

Robinson's  Principles  of  Mechanism 8vo,    3  oo 

Sanborn's  Mechanics  Problems Large  12mo,     i   50 

Schwamb  and  Merrill's  Elements  of  Mechanism 8vo,    3  oo 

Wood's  Elements  of  Analytical  Mechanics 8vo,    3  oo 

Principles  of  Elementary  Mechanics 12mo»    i  25 

MEDICAL. 

Abderhalden's  Physiological  Chemistry  in  Thirty  Lectures.     (Hall  and  Defren). 

(In  Press), 
von  Behring's  Suppression  of  Tuberculosis.     (Bolduan.) i2mo,     i   oo 

*  Bolduan's  Immune  Sera i2mo,     i  50 

Davenport's  Statistical  Methods  with  Special  Reference  to  Biological  Varia- 
tions   i6mo,  mor.,     i  50 

Ehrlich's  Collected  Studies  on  Immunity.     (Bolduan.) 8vo,  6  oo 

*  Fischer's  Physiology  of  Alimentation Large  i2mo,  cloth,  2  oo 

de  Fursac's  Manual  of  Psychiatry.     (Rosanoff  and  Collins.) Large  I2mo,  2  50 

Hammarsten's  Text-book  on  Physiological  Chemistry.     (Mandel.) 8vo,  4  oo 

Jackson's  Directions  for  Laboratory  Work  in  Physiological  Chemistry.  ..8vo,  25 

Lassar-Cohn's  Practical  Urinary  Analysis.     (Lorenz.) i2mo,  oo 

Mandel's  Hand  Book  for  the  Bic-Chemical  Laboratory i2mo,  50 

*  Pauli's  Physical  Chemistry  in  the  Service  of  Medicine.     (Fischer.) .  .  .  .  i2mo,  25 

*  Pozzi-Escot's  Toxins  and  Venoms  and  their  Antibodies.     (Cohn.) i2mo,  oo 

Rostoski's  Serum  Diagnosis.     (Bolduan.) i2mo,  oo 

Ruddiman's  Incompatibilities  in  Prescriptions. , 8vo,  oo 

Whys  in  Pharmacy i2ino,         oo 

Salkowski's  Physiological  and  Pathological  Chemistry.     (Orndorff.) 8vo,         50 

*  Satterlee's  Outlines  of  Human  Embryology i2mo,  ,       25 

Smith's  Lecture  Notes  on  Chemistry  for  Dental  Students 8vo,    2  sj 

16 


Steel's  Treatise  on  the  Diseases  of  the  Dog 8vo,  3  50 

*  Whipple's  Typhoid  Fever Large  i2mo,  3  oo 

Woodhull's  Notes  on  Military  Hygiene i6mo,  i  50 

Personal  Hygiene i2mo,  i  oo 

Worcester  and  Atkinson's  Small  Hospitals  Establishment  and  Maintenance, 
and  Suggestions  for  Hospital  Architecture,  with  Plans  for  a  Small 

Hospital I2mo,  i  25 

METALLURGY. 

Betts's  Lead  Refining  by  Electrolysis gvo.  4  oo 

Holland's  Encyclopedia  of  Founding  and  Dictionary  of  Foundry  Terms    Used 

in  the  Practice  of  Moulding 12mo,  3  oo 

Iron  Founder 12mo'.  2  50 

Supplement i2mo,  2  50 

Douglas's  Untechnical  Addresses  on  Technical  Subjects I2mo,  i  oo 

Goesel's  Minerals  and  Metals:     A  Reference  Book ; .  .  .  .  i6mo,  mor.  3  oo 

*  Iles's  Lead-smelting 12mo,  2  50 

Keep's  Cast  Iron gvo,  2  50 

Le  Chatelier's  High-temperature  Measurements.  (Boudouard — Burgess.)  I2mo,  3  oo 

Metcalf's  Steel.     A  Manual  for  Steel-users 12mo,  2  oo 

Miller's  Cyanide  Process 12mo  i   oo 

Minet's  Production  of  Aluminum  and  its  Industrial  Use.     (Waldo.)...  .  12mo,  2  50 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

Ruer '  s  Elements  of  Metallography .     (Mathewson ) .     ( I  n  P  ress. ) 

Smith's  Materials  of  Machines 12mo,  i  co 

Thurston's  Materials  of  Engineering.     In  Three  Parts 8vo,  8  oo 

part  I.     Non-metallic  Materials  of  Engineering,  see  Civil  Engineering, 
page  9. 

Part    II.     Iron  and  Steel 8vo,  3  50 

Part  III.     A  Treatise  on  Brasses,  Bronzes,  and  Other  Alloys  and  their 

Constituents 8vo,  2  50 

Ulke's  Modern  Electrolytic  Copper  Refining 8vo,  3  oo 

West's  American  Foundry  Practice I2mo,  2  50 

Moulders  Text  Book 12mo,  2  50 

Wilson's  Chlorination  Process 12mo,  i  50 

Cyanide  Processes 12mo,  i  50 

MINERALOGY. 

Barringer's  Description  of  Minerals  of  Commercial  Value.    Oblong,  morocco,  2  50 

Boyd's  Resources  of  Southwest  Virginia ^ 8vo  3  oo 

Boyd's  Map  of  Southwest  Virginia Pocket-book  form.  2  oo 

*  Browning's  Introduction  to  the  Rarer  Elements 8vo,  i  50 

Brush's  Manual  of  Determinative  Mineralogy.     (Penfield.) 8vo,  4  oo 

Butler's  Pocket  Hand-Book  of  Minerals Ibmo,  mor.  3  oo 

Chester's  Catalogue  of  Minerals 8vo,  paper,  i  oo 

Cloth,  i  25 

Crane '  s  Gold  and  Silv  er .     ( I  n  Press . ) 

Dana's  First  Appendix  to  Dana's  New  "  System  of  Mineralogy. ." .  .Large  8vo,  i  oo 

Manual  of  Mineralogy  and  Petrography I2mo  2  ~>o 

Minerals  and  How  to  Study  Them I2mo,  i  50 

System  of  Mineralogy Large  8vo,  half  leather,  12  50 

Text-book  of  Mineralogy 8vo,  4  oo 

Douglas's  Untechnical  Addresses  on  Technical  Subjects •. i2mo,  i  oo 

Eakle's  Mineral  Tables 8vo,  i  25 

Stone  and  Clay  Products  Used  in  Engineering.     (In  Preparation). 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Goesel's  Minerals  and  Metals :     A  Reference  Book i6mo,  mor.  3  oo 

Groth's  Introduction  to  Chemical  Crystallography  (Marshall) i2mo,  I  25 

17 


*  Iddings's  Rock  Minerals 8vo,  5  oo 

Johannsen's  Determination  of  Rock-forming  Minerals  in  Thin  Sections 8vo,  4  oo 

*  Martin's  Laboratory  Guide  to  Qualitative  Analysis  with  the  Blowpipe.  I2mo,  60 
Merrill's  Non-metallic  Minerals:   Their  Occurrence  and  Uses 8vo,  4  oo 

Stones  for  Building  and  Decoration 8vo,  500 

*  Penfield's  Notes  on  Determinative  Mineralogy  and  Record  of  Mineral  Tests. 

8vo,  paper,  50 
Tables    of    Minerals,    Including    the  Use  of  Minerals  and  Statistics  of 

Domestic  Production 8vo,  i  oo 

Pirsson's  Rocks  and  Rock  Minerals.     (In  Press.) 

*  Richards's  Synopsis  of  Mineral  Characters I2mo,  mor.  125 

*  Ries's  Clays:  Their  Occurrence,  Properties,  and  Uses 8vo,  5  oo 

*  Tillman's  Text-book  of  Important  Minerals  and  Rocks 8vo,  2  oo 

MINING. 

*  Beard's  Mine  Gases  and  Explosions Large  i2mo,  3  oo 

Boyd's  Map  of  Southwest  Virginia Pocket-book  form,  2  oo 

Resources  of  Southwest  Virginia 8vo,  3  oo 

Crane '  s  Gold  and  Silver .     ( I  n  Press . ) 

Douglas's  Untechnical  Addresses  on  Technical  Subjects i2mo,  I  OO 

Eissler's  Modern  High  Explosives 8vo  4  oo 

Goesel's  Minerals  and  Metals :     A  Reference  Book i6mo,  mor.  3  oo 

Irlseng's  Manual  of  Mining 8vo,  5  oo 

*  Iles's  Lead-smelting I2mo,  2  50 

Miller's  Cyanide  Process 12010,  i  oo 

O'Driscoll's  Notes  on  the  Treatment  of  Gold  Ores. 8vo,  2  oo 

Peele's  Compressed  Air  Plant  for  Mines.     (In  Press. ) 

Riemer's  Shaft  Sinking  Under  Difficult  Conditions.     (Corning  and  Peele) . .  .  8vo,  3  oo 

Robine  and  Lenglen's  Cyanide  Industry.     (Le  Clerc.) 8vo,  4  oo 

*  Weaver's  Military  Explosives 8vo,  3  oo 

Wilson's  Chlorination  Process iimo,  i  50 

Cyanide  Processes 12010,  i  50 

Hydraulic  and  Placer  Mining.     2d  edition,  rewritten i2mo,  2  50 

Treatise  on  Practical  and  Theoretical  Mine  Ventilation 12010,  I  25 

SANITARY  SCIENCE. 

Association  of  State  and  National  Food  and  Dairy  Departments,  Hartford  Meeting, 

1906 8vo,  3  oo 

Jamestown  Meeting,  1907 8vo,  3  oo 

*  Bashore's  Outlines  of  Practical  Sanitation 12mo,  i  25 

Sanitation  of  a  Country  House 12mo,  i  oo 

Sanitation  of  Recreation  Camps  and  Parks 12mo,  i  oo 

Folwell's  Sewerage.  (Designing,  Construction,  and  Maintenance.) 8vo,  3  oo 

Water-supply  Engineering 8vo,  4  oo 

Fowler's  Sewage  Works  Analyses 12mo,  2  oo 

Fuertes's  Water-filtration  Works 12mo,  2  50 

Water  and  Public  Health 12mo,  i  50 

Gerhard's  Guide  to  Sanitary  House-inspection 16mo,  i  oo 

*  Modern  Baths  and  Bath  Houses 8vo,  3  oo 

Sanitation  of  Public  Buildings 12mo,  i  50 

Hazen's  Clean  Water  and  How  to  Get  It Large  I2mo,  i  50 

Filtration  of  Public  Water-supplies 8vo,  3  oo 

Kinnicut,  Winslow  and  Pratt 's  Purification  of  Sewage.     (In  Press.) 

Leach's   Inspection   and    Analysis  of  Food  with  Special  Reference   to  State 

Control 8vo,  7  oo 

Mason's  Examination  of  Water.     (Chemical  and  Bacteriological) 12mo,  i  23 

Water-supply.  ( Considered  principally  from  a  Sanitary  Standpoint) . .  8vo,  4  oo 
18 


*  Merriman's  Elements  of  Sanitary  Engineering 8vo,  2  oo 

Ogden's  Sewer  Design I2mo,  2  oo 

Parsons 's  Disposal  of  Municipal  Refuse 8vo,  2  oo 

Prescott  and  Winslow's  Elements  of  Water  Bacteriology,  with  Special  Refer- 
ence to  Sanitary  Water  Analysis 12mo,  i  50 

*  Price's  Handbook  on  Sanitation 12mo,  i  50 

Richards's  Cost  of  Food.     A  Study  in  Dietaries 12mo,  i  oo 

Cost  of  Living  as  Modified  by  Sanitary  Science 12mo,  i  oo 

Cost  of  Shelter 12mo,  i  oo 

*  Richards  and  Williams's  Dietary  Computer 8vo,  i  50 

Richards  and   Woodman's  Air,  Water,  and  Food  from  a  Sanitary  Stand- 
point  8vo,  2  oo 

Rideal's  Disinfection  and  the  Preservation  of  Food 8vo,  4  oo 

Sewage  and  Bacterial  Purification  of  Sewage 8vo,  4  oo 

Soper's  Air  and  Ventilation  of  Subways.     (In  Press.) 

Turneaure  and  Russell's  Public  Water-supplies 8vo,  5  oo 

Venable's  Garbage  Crematories  in  America 8vo,  2  oo 

Method  and  Devices  for  Bacterial  Treatment  of  Sewage 8vo,  3  oo 

Ward  and  Whipple's  Freshwater  Biology.     (In  Press.) 

Whipple's  Microscopy  of  Drinking-water 8vo,  3  50 

*  Typhod  Fever Large  I2mo,  3  oo 

Value  of  Pure  Water Large  I2mo,  i  oo 

Winton's  Microscopy  of  Vegetable  Foods 8vo,  7  50 

MISCELLANEOUS. 

Emmons's  Geological  Guide-book  of  the  Rocky  Mountain  Excursion  of  the 

International  Congress  of  Geologists Large  8vo,  i  50 

Ferrel's  Popular  Treatise  on  the  Winds 8vo,  4  oo 

Fitzgerald's  Boston  Machinist i8mo,  i  OD 

Gannett's  Statistical  Abstract  of  the  World 24mo,  75 

Haines's  American  Railway  Management 12mo,  2  50 

*  Hanusek's  The  Microscopy  of  Technical  Products.     (Winton^ 8vo,  5  oo 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute   1824-1894. 

Large  i2mo,  3  oo 

Rotherham's  Emphasized  New  Testament „ . . , Large  8vo,  2  oo 

standage's  Decoration  of  Wood,  Glass,  Metal,  etc 12mo,  2  oo 

Thome's  Structural  and  Physiological  Botany.     (Bennett) 16mo,  2  25 

Westermaier's  Compendium  of  General  Botany.     (Schneider) 8vo,  2  oo 

Winslow's  Elements  of  Applied  Microscopy 12mo,  i  50 


HEBREW  AND  CHALDEE  TEXT-BOOKS. 

Green's  Elementary  Hebrew  Grammar i2mo,     i  25 

Gesenius's  Hebrew  and  Chaldee  Lexicon  to  the  Old  Testament  Scriptures. 

(Tregelles.) Small  4to,  half  morocco,    5  oo 

19 


OF  THE 

{    UNIVERSITY  ) 

OF 


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